Patterns.dev
patterns.dev546 points by handfuloflight 21 hours ago
546 points by handfuloflight 21 hours ago
Design patterns can be really helpful. In my previous job I worked on enterprise .NET applications. It made sense to use common patterns, because most applications were big and the patterns made it easier to understand unfamiliar code, within an application but also across different teams and applications. New projects looked familiar, because the same style and the same patterns were used.
Now I'm working on an old (+10 years) JS application. Similar patterns were implemented, but in this case it's not helpful at all. The code looks very corporate and Java EE style, with a ton of getters and setters (`getName() {}`, not `get name() {}`, factories, facades, adapters, etc, etc. It's usually completely unclear what the benefit of the pattern is, and code is more complicated, for instance because creating new instances of business objects is split into `Object.build` which calls `new Object`, with no guidelines at all what part of the initialization should be in `build` and what should be in the constructor.
The gist of my comment is that patterns can be useful, but usually they're overused and if you implement one without understanding why and without benefiting from faster understanding the code because the pattern is applied consistently over multiple instances, the result is worse than just implementing what you need in a readable way (YAGNI).
I would put it slightly differently: Patterns (including anti-patterns) happen whether you call them such or not. Any developer will sooner or later come up with patterns like Adapter or Builder or Composite or Iterator. In that sense, patterns are not invented, but discovered. The benefit of design patterns is to be able to communicate these discovered patterns, and to define agreed names for them, so that you don't have to describe the pattern each time you talk to another developer, but can refer to it by a well-understood name. (Or when not yet well-understood, can refer to the corresponding pattern description.) It extends the language we use to talk about software design.
The point of design patterns is less about the individual patterns, than about having "design pattern" as a general concept of coding patterns relevant to software design, that you name and describe because they keep reoccurring.
I would go even further.
For me design patterns are more of vocabulary than a tool.
It's not about - hey I found this book and we'll be using these building block from now on - rather, it's about having words that everyone immediately recognizes and associate with exact same ideas.
Yes and no. Some patterns exist because the language isn't expressive enough. This is one reason why the patterns made sense in the OP's .NET programs, but made less sense in JS. JS simply doesn't require as much ceremony for some things because it's dynamically typed and reflection kind of comes for free.
I would say that reflection in JS is terrible compared to .NET. You can only just barely figure out what is in an object, but it's a hell of a time figuring out what any of those things can do. I wouldn't so much as call what JS does "reflection" any more than "making objects out of poorly implemented hashmaps."
>You can only just barely figure out what is in an object
There's a couple really well documented and understood ways of doing this in the language. I'm not sure what you're specifically referencing without more information.
>I wouldn't so much as call what JS does "reflection" any more than "making objects out of poorly implemented hashmaps."
Is this anymore different than .NET deriving everything from a base `System.Object`[0] type?
Also, what is missing in JS reflection wise that you can't do that would make sense for its environment? (namely, this excludes compile time reflection stuff I know .NET can do, it wouldn't make sense for a scripting language as it currently is)
[0]: https://learn.microsoft.com/en-us/dotnet/api/system.object?v...
In JavaScript, one can tell if an object has a method by iterating over the object keys and seeing if the value is `instanceof Function`.
But that actually tells you very little. You might be able to tell that it takes a certain number of parameters, if you are running on a system that implements Function.prototype.length. But you will have no way of telling what the arguments to those parameters should be, or even what they were even named. There's no way to tell if the function is a method that needs to be `.call()`ed with a value for "this", or if it's just a function that happens to live in an object literal, or if it's actually a class constructor that must be called with `new`! And there is certainly no way to tell whether the function returns a value, say nothing about the type of value it returns.
With .NET reflection, I can do ask those things I lament missing in JS, and guarantee the type safeness of it.
"Javascript" === "Chaotic neutral lisp"
lisp to me is (1) the language itself is a lists of lists (2) defmacro lets you manipulate those lists of list at compile time. JS doesn't this do either of these at all AFAICT and so is absolutely nothing like lisp.
Most lisp programs are about writing DSLs using defmacro.
What's the similarity to lisp except that both are programming languages?
Yeah, I don't like the comparisons of JS to Lisp, because I think they mostly center on the existance of the map and filter methods of Array. To me, that's just not what Lisp is about. C# has map/filter/etc, and we don't say C# is-a Lisp.
And there are many other such features that were once unique/unique-ish to Lisp, that were major selling points for using Lisp at the time, but are now pretty common across a very diverse set of languages. Garbage collection being one. Higher order functions being another.
Lisp's big idea that stuck to being unique to Lisp is homoiconicity. It's the one thing that continues to be valuable enough to warrant using Lisp, despite everything else that has been stolen and copied.
Of course, not that I ever used Common Lisp, and not that I use Racket anymore. I enjoyed the hell out of programming in Racket. Up until the point I needed to access a database. Man, who's got time for that Jankasarous Rex? But I really would love a homoiconic language for the .NET CLR. That would be pretty sweet.
A lot of patterns only make sense in languages like C# or Java, which are inflexible by design. You have two hierarchical trees (inheritance and namespaces) that you have to work around. With something simpler like C, Go, JavaScript, you don’t have those obstacles and a solution can be way simpler to implement.
Some patterns in the GoF book only apply to C++/Java as they were in 1994, but I don't see any reason why other languages would have no useful patterns. The Linux kernel (C) is full of patterns for example.
Funny thing, Peter Norvig also has this position, that patterns only apply to languages like Java, but his book on Lisp and the Python course he had on Udemy (?) are super-pattern-y.
How do optional inheritance and namespaces (which you can ignore to use a single global namespace) make a language inflexible? If anything, these traits make your language more powerful, not less.
Somewhat true - I usually find that in these languages the patterns are there they are just less obvious.
This is a common thing I see when developers that come from an OOP enterprise environment familiar with Java, C#, etc. do JavaScript, they try to use all the same patterns, default to classes for everything. It just doesn't fit the language.
It was fascinating to me to see JavaScript add the class keyword, have it be widely adopted thanks to React, then just a few years later seeing `class` in JavaScript code is, as you said, a clear sign a Java/C# dev was here.
I haven’t done JavaScript in a long while, is using ‘class’ not a favored way of writing JS these days? I wrote JS heavily pre-class, and never really got comfortable using it before switching my focus to other languages.
The poster you're replying to is plain wrong, using "class" is ubiquitously common in the javascript/typescript world, it's the idiomatic way to create classes, and it has better semantics than trying to use prototypes. You might compile away the class keyword for compatibility, though.
Yeah, I've seen (okay, and been responsible for) a lot of "the road to hell is paved with good intentions" due to jumping to some pattern or other because, well, it feels like the right thing to do. It makes the code cleaner at delivery time, and is usually very intuitive when the design is fresh in your mind. But IME it doesn't take long before that freshness goes away, and the next time you look at it (let alone anyone else) you find it hard to follow the logic anymore. Usually "constructing" the pattern and "executing" the pattern are in different places in the code, and there's not a straightforward way to mentally step through one without continually cross-referencing the other. At some point you wish you'd just written one long switch block that you could step through.
And that's all before new requirements that break the pattern, or other engineers that don't have time to grok the design and hack in something that looks like a switch block for their thing, which eventually takes over most of the code anyway.
I see a lot of comments about how patterns are useless from people writing toy apps or at least ones that never had to deal with really enterprise scale stuff. So for me they are like people building a shed screaming at people building sky scrapers that no one ever needs to pour so much concrete to form a foundation.
Parent comment is not like that.
People were shifted from Java to Javascript and kept the Java patterns and maybe the organization had standards requiring their use.
design patterns are a language, it's just that the programming language they're being implemented in doesn't support them natively.
e.g. observer pattern in java is what, [array of functions].forEach() in js? not worth calling that by name. another example, singletons - in Python, it's just a module (caveats apply obviously, but if we apply them, some also apply in java).
this is why designing a minimal language to make it 'simple' is misguided: you'll end up having to reinvent the design pattern language anyway. there are good reasons to design a simple language, but simple for the sake of simple is missing the point.
Does anyone remember the Yahoo design patterns library? It was mostly for UX pattern (eg: ways to "Rate an object") and it was really good.
Almost 20 years ago.. damn.
https://creativecommons.org/2006/02/14/yahoodesignpatternlib...
https://web.archive.org/web/20060221111812/http://developer....
They had a great comparison of the different behaviors leaderboards could encourage in users.
Not quite the same thing, but there's this incredible (open source) project called The Component Gallery that is basically just a repository of UI components across 93 (currently) different design systems. It's an incredible resource if you're building a component from scratch and either want some design inspo or technical advice. Many of the design systems have thorough guidelines for a11y/ARIA best practices that I've learned a ton from
Amen! The terms "accordion" and "carousel" were really codified by the pattern library. Establishing a common vernacular definitely accelerates things.
Oh, the second link is amazing. I love the old web, and that brought a lot of nostalgia.
YUI was ahead of its time as well
And it spawned ExtJS. Which could have been React, but they messed up. Literally they built a faster Facebook app 'Fastbook' in 2012.
Short history lesson:
https://medium.com/hackernoon/the-rise-and-fall-of-ext-js-c9...
In August 2006, a guy by the name of Jack Slocum (now CEO of Alta5) began to blog of his experiments with YUI. Over time, these experiments became more complex and Jack would start to bundle them into what would later be named YUI-ext (Yahoo UI extensions) — the precursor to Ext JS (Extensible JavaScript).
Jack Slocum’s blog was used to communicate his vision for YUI-ext and garnered community support from around the world. The release of the Grid component for YUI-ext would forever change the trajectory of the library and the community as the GridPanel would become the core UI component for many applications to come.
Throughout its early life, Jack continued to build upon YUI-ext by adding features to the framework, such as animations, Modals, Tab Panel, Resizable elements and a layout manager that greatly expanded upon the YUI framework. These components would seldom extend the YUI library and had their own rendering functions.
YUI-ext created a foundation for web programmers unlike anything the world had seen before and many developers flocked to the framework and invested in the newly formed community. The net result was the explosive expansion of YUI-ext.
From YUI-ext to Ext JS In January 2007 we found Jack extremely busy to push out YUI-ext 0.40 and it is this version where we find the namespace of the framework change from YAHOO.ext to a much simpler Ext (pronounced “ekst J S” or “E-X-T J S” by some of us old-school community members).
February 2007, Ext JS 1.0 was being developed in tandem with a new website, ExtJS.com. In April 2007, the launch of ExtJS.com was announced to the community along with the release of Ext JS 1.0.
https://web.archive.org/web/20230222210535/https://jackslocu...
For those that don’t know, Ext JS was one of the first JavaScript frameworks in the early days of Web 2.0. It was the first framework to offer a complete package of everything needed to build full-fledged applications using just JavaScript in a web browser. At one point, it was used by over 2 million developers worldwide, 70% of the fortune 500, and 8 of the top 10 financial institutions. It was years ahead of everyone else, open source, and had an incredible community of passionate people contributing to its success.
As that success grew, so did the number of copycat competitors. They eventually started taking the code and assets and embedding them into their own frameworks. Adobe embedded it in Cold Fusion and other competitive frameworks followed their lead without any contribution to the framework or community.
At the time the thought of competing directly against a behemoth like Adobe was scary. How could they take our product and offer it as their own? I took what I thought was the right action to “protect” Ext JS from being “stolen” by changing to a more restrictive license. That was a huge mistake.
Looking back in hindsight, without the fear, I have a much clearer picture. I see what truly made Ext JS great was not the code - it was all the people who loved, contributed and supported it. As we worked on making our own dreams a reality, we helped others do the same, sharing our knowledge, code, and solving tough challenges together.
That is what really mattered — our community. That is what I should have protected, not the code. You were my closest friends. I am sorry I changed the license after we all came to an agreement on the first license. That was a breach of integrity and you deserved better. I would do it differently if I could.
we often forget how great Yahoo engineering was back in the day, sad it was destroyed by bad management and horrible business cases prioritization
for some reason I remember him being related to YUI, but I learned JS from Douglas Crockford, one of the best lectures from the old days of JS.
Looks great, time to add it to my bookmarks.
Anyone has other sites like these to share?
- Domain-driven design, design patterns, and antipatterns
- Refactoring and Design Patterns
- Standard Patterns in Choice-Based Games
https://heterogenoustasks.wordpress.com/2015/01/26/standard-...
Here be dragons. People trying to pattern-match their problems to design patterns can waste a lot of time and effort over many years. Use responsibly.
To your point, everything we do is context-sensitive and patterns are revealed by abstracting context.
I posted this elsewhere in this thread:
Great meta resource for building UI components.
Design patterns and component libraries are a bit related but they're pretty different concerns ultimately.
It's more of a meta resource. Many of these design guidelines go in depth on accessibility best practices and UI patterns
- Java Design Patterns
Microsoft's cloud design patterns are quite well-written IMO, if you're into that kind of thing
https://learn.microsoft.com/en-us/azure/architecture/pattern...
The OG site for patterns is of course the Portland Pattern Repository. I believe Ward Cunningham invented wiki for this purpose initially!
I’ll make a plug for aep.dev, which is a collection of API design best practices and assorted tooling
Google has something similar:
AEP began its life as a fork of AIP! We’ve got a bunch of ex-Google folks on the project, including the former API Lead at Google.
+1 for refactoring.guru, find it really useful whenever i want to refactor some pre-existing code. Only wish they had a physical book!
I find that the more senior you become, the less you rely on software design patterns.
Juniors often think that learning design patterns is some kind of career hack which will allow them to skip ahead a decade of experience... There is some utility in many design patterns but the problem is that juniors often miss the nuance and the motivation behind the patterns and they tend to misuse them; often creating more complexity than they would have created had they not used design patterns.
There are situations where design patterns may be useful but they're much more rare than most people think. A lot of juniors seem to think that every problem requires them to apply a design pattern from their toolbox. They try to frame every problem within the constraints of design patterns that they know. This can create problems.
In fact, there are many coding patterns which are far simpler than 'design patterns' and much more useful, but nobody talks about them because they're too trivial to discuss. For example, I've seen people write code which relies heavily on design patterns but then that same code uses an O(n^2) nested loop to find items that are common between two arrays. There is a simple 'pattern' you can use to store the items of the first array in a Set or HashMap and then finding common items is O(n) because Set and HashMap lookups are O(1)... Very useful pattern but I don't believe it has a name. I use it literally ALL the time. The idea of storing intermediate state in some kind of HashMap is a game-changer IMO but there's no name for that pattern of coding. In general, knowing what data structure is most appropriate for various scenarios is a game changer... But still, don't abuse. Basic data structures like arrays are fine most of the time.
Anyway, it's good to absorb the wisdom behind some design patterns but you should not try to fit every problem to them and dont say stuff like "For this problem, I applied Design Pattern X" - If you do, senior engineers will know you're a junior. If you use a design pattern correctly, it will probably not look exactly like in the textbook. It's kind of hard to give it a name. It may be a mix of patterns. It's the principle that counts. Reality is too complex for rigid design patterns.
On the other hand, some design patterns are too common and obvious to deserve a name. For example, the factory pattern is super common... I use it all the time but it's so basic and obvious that I will sound like a total noob if I go around calling my function "socket factory pattern"... I will call it "Utility function to obtain a socket" or something. I will never refer to it as a factory pattern, it's a bit cringe.
I see it as a common vocabulary to talk about tools. It's simpler to say "I made a singleton" than to describe it.
Just like we have words for a nail, a screw, a hammer. If you had to say "I used a tool that I find works well with nails", that would be annoying and ambiguous.
Now of course, if you quickly screwed something with your swiss-army knife and a junior came and told you that this is wrong, because you should always use a proper screwdriver, and therefore you should rent a car and drive 30min to go buy it right now, you would kindly tell them to fuck off. Doesn't mean that there is no value in the concept of a screwdriver itself.
You point out the cultural issue that this creates and sweep it under the rug, violently.
The thought model complicates the process of writing new code, "what pattern do i need here?" and the perception of existing code, "oh this is pattern X, why isn't that communicated clearly?". The truth is that design patterns are at best stagnant in quality and quantity over time (GoF is over 30 years old!), but the quantity and quality of problems is infinite.
I've thought in patterns quite some time in my early career. With my colleague back then everything was an pattern and we were kind of in sync with that approach. But it quickly falls apart if you have peers that are less try hard on it. You can spend days, weeks, months to study design patterns and then have to explain it to someone in 5 minutes that simply doesn't care. I can't blame anyone to not care, so that has to be accounted for.
I think the common language argument is tempting, but also too stressed. Good and useful programming knowledge is bound by reality. An integer is a indisputable thing that is always useful. A "singleton" is just a fancy rephrasing of "global state".
I did not mean "everybody has to learn the vocabulary". I meant the opposite, actually: it's fine not to know the word for the tool (I don't enjoy reading about patterns just to learn about patterns, it's not my thing at all).
Say I build a tool that makes it easier for me to drive a nail and call it a "Naildriver". If I show it to a colleague, they may be able to tell me "oh, this is generally called a hammer!". Maybe they will even tell me how I may improve my hammer, because they happen to like to learn about hammers in their free time. Or maybe now that they said it's a known concept, I will enjoy reading about hammers online (doesn't mean I will now read the entire encyclopedia of tools).
The fact that there is a name for the concept ("it's called a hammer") does not say you have to know the word. It's just useful to have a word for it, because then we can reference it in discussions and share knowledge about it more easily.
The other thing that design patterns allow, is to learn pitfalls, applications and other attributes about them.
To keep in your analogy, if you have a 3KG naildriver with a 2m handle you'll quickly find out that driving nails into a drywall with that leaves you with no wall. And that it's a bad idea to use a "Naildriver" to drive these "spiralled-slothead-nails" (aka screws) into wood.
But with a common language, such as design patterns, you can easily learn where they are good, what their limits are, in what cases other patterns fit better, and what pitfalls to avoid and so on.
If I search the web for "why is it so hard for my naildriver to drive in spiralled-slothead-nails" I'll get zero results. But when I search for "why is it hard to hammer in a screw" I'll get good results. May sound like a silly example, but for me that sillyness illustrates how obvious designpatters should be.
I totally agree with that!
And it doesn't mean at all that everybody should learn the whole encyclopedia of tools by heart. But having it formalised somewhere is useful: as soon as someone tells me "what you're trying to do sounds like this design pattern", I can start searching and reading about it.
Of course if that someone tells me "you suck, you should know that there is a design pattern for that because you should read about design patterns every night before you go to sleep", it will be different :-).
I have mixed feelings about this.
I think Julian Assange once said he would refer to things in discussion just as "Tomato" (or similar), in discussion to have a shortcut for something unnamed with some meaning. We do this all day in programming, we give a complex component a name and it means a lot more then just the actual word. The problem is that this specific meaning is often not universal, it's contextual.
If you take a hammer, an integer and design patterns, the latter is the least universal thing. They depend on domain, context and conventions, and can change quite a lot depending on the language. Removing hammers and integers from the world would cause collapse, removing design patterns would do almost nothing.
I guess the active celebration of design patterns as a catalogue of general wisdom is my primary issue here. I'd welcome any project/team/company that maintains a catalogue of their individual "patterns". But a universal source of truth has too much bible flavor to me. (Oh it also dictates OOP by default which renders it's inherent "wisdom" completely useless in many languages)
> For example, I've seen people write code which relies heavily on design patterns but then that same code uses an O(n^2) nested loop to find items that are common between two arrays. There is a simple 'pattern' you can use to store the items of the first array in a Set or HashMap and then finding common items is O(n) because Set and HashMap lookups are O(1)... Very useful pattern but I don't believe it has a name. I use it literally ALL the time. The idea of storing intermediate state in some kind of HashMap is a game-changer IMO but there's no name for that pattern of coding.
This is a "hash join" in relational databases. You can see it in the query planner output of at least postgres.
I wouldn't say it's cringe. A factory is a factory. Calling it that in the code may not be the best idea, but having the shared vocabulary is nice. Basically, patterns work well when they're descriptive rather than prescriptive.
There are two cases that are unique though: state machines and visitors are so much things on their own, that you'll use those names almost every time you run into the pattern.
The visitor pattern is my go to example for patterns, that you don't really need, when you have a language that has first class functions, which implies among other things, that you can pass functions as arguments, like you can pass anything else.
The magical "visitor" pattern becomes nothing more than simple callback passing or passing a function, which is one of the most natural things to do in a modern programming language.
State machines at least are useful as a conceptual thing, to find a way to think about how one solves a problem, no matter how they are ultimately implemented in the end.
I've always seen the visitor pattern as a poor-mans pattern matching. How do you solve the same thing with callbacks?
> A factory is a factory.
Yes, but what about factory factories? https://factoryfactoryfactory.net
> For example, I've seen people write code which relies heavily on design patterns but then that same code uses an O(n^2) nested loop to find items that are common between two arrays. There is a simple 'pattern' you can use to store the items of the first array in a Set or HashMap and then finding common items is O(n) because Set and HashMap lookups are O(1)... Very useful pattern but I don't believe it has a name. I use it literally ALL the time. The idea of storing intermediate state in some kind of HashMap is a game-changer IMO but there's no name for that pattern of coding.
Isn't this called 'dynamic programming'? It's actually a habit people should pick up when grinding leetcode.
No, dynamic programming is when you split your bigger problem into a smaller one + 1 step to get to your bigger size. Then apply that recursively until you solve the trivial problem at the end and get back the answer for your original problem size.
If you already have Sets handy - why not use the Set Intersection? (Assuming the Set implementation has that capability).
Putting both contents (lists, arrays, whatever you have) into sets, and then calculating the intersection might be more expensive than building the intersected set right away sourcing both non-set contents, I imagine. Though it would probably be easier to read and understand. But that can be solved by naming of functions that process the 2 non-set things.
the actual software design patterns, unbiased by language/particular-usage, are subtle. i would go as far as say that there are also "design-patterns"-usage patterns.. and those might be even more subtle. e.g. what is/constitutes "interpreter", and when to use one, and when/if one is being used behind-the-scenes. Sometimes it is a single piece that is easily pinpointable. Sometimes a whole (sub)system behaves like one (e.g. event-sourcing stuff) but it's not easily cut into this is this, that is that.
But anyway, this site seems javascript/frontend wanna-bees oriented.. please don't take those tutorials as mantras-to-follow-at-any-rate. See if you can take the knowledge and move on.
A very good book, besides the GoF one, is the "Organisational patterns book by James Coplien, Neil Harrison" [1]. It contains some of the GoF *plus* all the non-technical ones, and they are bundled together - as software making is not just the coding.. i have the list of those patterns essences (patlets) extracted, here the link - https://www.svilendobrev.com/rabota/orgpat/OrgPatterns-patle...
edit: it's from ~2003-5 and images are missing. May need to scan them from the book. Closest i found is [2], at least to get some idea
[1] http://www.amazon.com/exec/obidos/tg/detail/-/0131467409/
[2] https://www.scrumbook.org/book-outline/history-of-the-patter...
For your example, if both lists are small enough, the constant factor on the cost of creating the hashmap eliminates any advantage you could have. Anyway, it's not like most places were I've seen a nested loop used for search the developer had cared. Today I am in a bad mood.
I have to touch some of the most unnerving modules in a legacy project and everything is a trap. Lot's of similar repeated code with ugly patterns and some big brain trying to hide the ugliness with layers and layers of indirections and inheritance, and calling it clean because there is a factory class. The biggest joke? each implementation have a different interface for key methods, so later you to check what instance got created.
I want to keel myself. Anyone could assist me in a seppuku?
Don't kill yourself. Stop and leave. Every day you will build up a tiny bit more resentment and then first you will become more cynical but eventually you will burn out. Be proactive and leave this behind, move on with life.
What about the social / communication aspect ? Having a common vocabulary of pattern may help reduce cognitive load when reading others code. Just a soft opinion because I assume it's the reason frameworks and conventions help teamwork. Less per-context custom solutions.
It really depends. If under the guise of "best practices" and "patterns" a team creates an unmaintainable, not easily extensible mess, then all this community aspect was good for exactly nothing but shoulder patting. If instead pattern are used sparingly, where they actually make sense, then sure, it can help.
We need to keep in mind, that the most composable concept in computer programming is the pure function (or maybe a mathematical "relation", if we want to abstract further). Not a mutating object. Not some constellation of objects that constitutes a pattern. Those are merely special cases.
I am currently developing a GUI application. Most of the classes in my code are classes, that are custom widgets. The GUI framework is OOP, so that is kind of infectious for the rest of the code. Still I try to keep some stuff separately as pure functions. Probably will outsource more stuff like that into completely self sufficient functions. The only pattern I have so far in the whole application, is a mediator, which I use as a way to have objects register themselves as listeners to specific events and for other objects to send these events to anyone who will listen. That way objects don't need to know, which other objects are interested in learning about some event. Could I have built in some factories and whatnot? Surely I could have, but there would have been very little, if any benefit. Even the mediator only exists, because the GUI framework does not have a way to send events that include data, so I need a way to do that. Otherwise I could even get rid of that pattern as well.
In this way pattern are useful for when you really need them, but these OOP pattern by themselves, without context, don't really have a value. No code becomes better by building in more patterns, unless the situation requires such a solution.
> Very useful pattern but I don't believe it has a name.
This is an instance of “use the right data structure for the job”. To me it has little to do with architectural design (where design patterns live), but it has to do with algorithmic design.
For webdev especially everything I do is basically singletons... For UI state management its just perfect and that's about the hardest thing in web dev. Also easy to recover state with, in a SPA if a user refreshes the site. Or control whether a modal is open or not. Easy to centralize logic too... Never looked into any other patterns as a lot of them seem like bloat.
Agreed! The problem is that some 'seniors' never cared to learn patterns in the first place. That’s a huge problem for frontend, where we have increasingly complex architectures and people with very little experience with design.
Even some principles aren't known. I always recommend the book Head First: Design Patterns. It's in Java, but the lessons can be applied in every language.
Unfortunately, we are in a 'post-knowledge' era... I don't know how we can keep things up at this pace.
> It's in Java, but the lessons can be applied in every language.
I can only discourage anyone from applying Java patterns all over the place. One example in JavaScript: There was a functionality that required some parameters with default values. The plain solution would have been:
function doStuff({ x = 9, y = 10 } = {}) { ... }
I've read that book, and it felt very childish and condescending.
Design patterns cannot be applied in every language. While some patterns are applicable everywhere, many of them provide replacements for missing language features. For example, the Builder pattern is not very useful in languages with default parameters and named arguments.
I'm not sure what Builder would have to do with default parameters and named arguments.
Builder is extremely useful to pair with a parser, e.g. SAX. The parser parses the input, and the builder then decides what to do with it.
Here is an example of the Builder pattern that illustrates my point: https://www.baeldung.com/java-builder-pattern#bd-classic-bui...
Let’s remove the category argument and you get this:
Post post = new Post.Builder()
.title("Java Builder Pattern")
.text("Explaining how to implement the Builder Pattern in Java")
.build();
Post post = new Post("Java Builder Pattern", "Explaining how to implement the Builder Pattern in Java", null);
Post post = new Post(title: "Java Builder Pattern", text: "Explaining how to implement the Builder Pattern in Java");What's interesting about frontend is that there are two ways to evaluate it: by how it looks and how it's written.
It definitely biases how people evaluate llms. Many cite Claude as their favorite llm for generating frontend code, but I suspect that many people prefer it because the output is prettier, rather than better composed.
Design patterns are language independent, but a lot of the ones many Java devs focus on are a bit meh.
In a world with only assembly language, for instance, it’s a bit like making a big deal about a “guarded repetition” pattern (aka a while loop).
Eg in Lisps, a lot of patterns become one-liners. At that point these patterns become a “can you write decent Lisp” question[1].
In my senior year of college two decades ago, I needed one or two credit hours to finish up, and I signed up for a once per week software patents (as in, intellectual property, I thought) course. It turned out to be a patterns course taught by none other than Ralph Johnson and the text was his famous Gang of Four Design Patterns book. Happy accident, it turned out to be among the most professionally useful courses I ever took.
https://en.wikipedia.org/wiki/Ralph_Johnson_(computer_scient...
"Design Patterns are a sign of missing language features".
https://wiki.c2.com/?AreDesignPatternsMissingLanguageFeature...
https://norvig.com/design-patterns/design-patterns.pdf
https://medium.com/@letsCodeDevelopers/your-design-patterns-...
This is a nicely laid out collection of tutorials, but I'm sad that collections like this have drifted away from the very deliberate structure that A Pattern Language introduced. While patterns weren't invented by Alexander and co, they did inspire a lot of what we see in tech these days, inherited via design patterns etc.
In A Pattern Language, each pattern is hyperlinked to other patterns in a kind of hierarchy, where larger patterns (like "house cluster") are broken down into smaller constituent parts ("main entrance") all the way to quite granular details ("low doorway").
This is because you can't just take a pattern on its own; it forms part of a larger whole.
Tech pattern books often focus on small recurring structures (e.g. "command pattern" from this site), but not how they help create some larger pattern, or in the other direction, what are the smaller patterns that help create them.
This sounds like a lot of hard work of course, which is why people don't do it.* I would love to see this accomplished though. If only I had an extra 36 hours in each day.
One thing that A Pattern Language is also great at is motivating each pattern with a specific problem or symptom. This site seems to do a decent job at that, though some problems seem... kind of weakly motivated. For example, the above mentioned "command pattern" is motivated by "what if we need to rename a method?" which... is pretty weak tbh.
*EDIT: also because fitting patterns into a whole, maybe unavoidably, will promote a perspective, or a way of building a whole system. A pattern book for web applications written from an HTMX point of view would be a very different book to one written from a React slant. Maybe one pattern language can accommodate both sets of technologies, or maybe not.
Here's an excerpt from APL showing what I mean about the connections to the other patterns. This isn't the whole pattern, there's a lot between the problem statement and summary. Annotations in brackets are mine.
---
Short Passages (132)
[Context, or pre-links]
The Flow Through Rooms (131) describes the generosity of light and movement in the way that rooms connect to one another and recommends against the use of passages. But when there has to be a passage in an office or a house and when it is too small to be a Building Thoroughfare (101), it must be treated very specially, as if it were itself a room. This pattern gives the character of these smallest passages, and so completes the circulation system laid down by Circulation Realms (98) and Building Thoroughfare (101) and The Flow Through Rooms (131).
[Problem statement]
Long, sterile corridors set the scene for everything bad about modern architecture. In fact, the ugly long repetitive corridors of the machine age have so far infected the word "corridor" that it is hard to imagine that a corridor could ever be a place of beauty, a moment in your passage from room to room, which means as much as all the moments you spend in the rooms themselves.
[Pattern contents here]
[Pattern summary]
Keep passages short. Make them as much like rooms as possible, with carpets or wood on the floor, furniture, bookshelves, beautiful windows. Make them generous in shape, and always give them plenty of light; the best corridors and passages of all are those which have windows along an entire wall.
[Elaboration, or post-links]
Put in windows, bookshelves, and furnishings to make them as much like actual rooms as possible, with alcoves, seats along the edge - Light on Two Sides of Every Room (159), Alcoves (179), Window Place (180), Thick Walls (197), Closets Between Rooms (198); open up the long side into the garden or out onto balconies - Outdoor Room (163), Gallery Surround (166), Low Sill (222). Make interior windows between the passage and the rooms which open off it - Interior Windows(194), Solid Doors With Glass(237). And finally, for the shape of the passages, in detail, start with The Shape of Indoor Space (191)
When overused these kind of "patterns" always lead to slow and hard to grasp code that is a nightmare to maintain.
My experience is that they are best discovered independently as a way to abstract code, and let them come naturally to solve a problem. So for most things in Dev, if you do something prematurely you might end up with a good solution for a non existing problem.
The ones that actually match POSD (deep modules, small interfaces, lower complexity) and work great with plain functions are:
Module Pattern
Factory Pattern (factory functions)
Mediator / Middleware Pattern (as function pipelines)
Hooks Pattern (custom hooks, generalized)
Container / Presentational Pattern (implemented with function components + hooks)
Everything else is either neutral, UI-only, or fights POSD (Singleton, Mixin, etc.).
Patterns from that page you should treat skeptically for POSD
From Patterns.dev, for your POSD-style codebase I’d avoid or downplay:
Singleton Pattern → encourages global state and tight coupling. Patterns
Mixin Pattern → tends to increase interface surface and make dependencies opaque. Patterns
Observer Pattern → powerful, but event-based wiring can obscure data flow and increase “system complexity” (classic POSD warning). Patterns
What does POSD stand for?
I'm assuming John Ousterhout's book A Philosophy of Software Design [1], which I would recommend reading before reading about design patterns, because it's more fundamental.
I'm assuming Philosophy of Software Design but I've never seen anyone blatantly presume it's an implicit initialism
this site reads like its 2017
its low quality, breadth but no depth
more important is to deeply understand the basics of working with immutable data. try writing applications with no for loops or forEach (and actually use the array methods as they are intended), no cloneDeep hacks and obviously no direct property mutation, always create a new object.
in real world you still use for loops plenty, but as a junior its good to see what its like to live without it for a while.
I've used Clojure/Script in the past and it's good to enforce working with immutable data.
Immutable.js has similar data structures but it's not the standard way of doing things and uglier to debug.
Using standard objects, immutability is not enforced in JS and throwing a few Object.freeze calls won't change that so we lose half the benefits that Clojure would bring: parallel/concurrent programming benefits, easier deep equality checks, performance...
If the code is not performance sensitive and can run in a single thread, simply "not mutating some of the mutable data" is a start for someone interested in immutability. That's what ramdajs does, it doesn't invent new data structures or freeze objects but simply returns new ones.
Only a few functions from ramdajs are actually useful in 2025 since JS has evolved with things like array/object destructuring and "..." but in any case it's an inspiring library.
I've used these things. IME, nowadays it's not worth the bundle size to bring in these libraries. map/filter seems quite optimized, {...obj} is fast since its only shallow. Yes it does come down to practices vs better libraries, but in practice, it's fine IME
One thing to note, i was very excited that we have a bunch of lazy methods on Iterator protocol, but they are slow as shit as of earlier this year.
I wrote a parser a year ago with extreme use of .map (every step of processing was cloning the tokens), and i thought, let's migrate it to lazy iterator - it got ~10x slower :(. The compile time was fine for my use cases, so i didn't give immutable-js a try, but it was a surprise
I did some benchmarks on map+filter vs mutable for of + push, and on firefox up to 200-300 elements map+filter is actually faster (unforunately not on chrome).
Of course, its not the best, but my experience is that modern js engines are fast enough for most use cases to not have to bring in any libraries anymore
although this article does get me thinking of documenting the “patterns” i use, and why.
I wish people would stop promoting the singleton pattern: in almost every case I’ve seen, singletons are unnecessary tech debt and solve a problem that’s better solved with some form of dependency injection (and I don’t mean the XML/YAML monstrosities various frameworks force on you but rather constructor arguments or factory functions)
The site is not "promoting" the singleton pattern. In fact, there is a "Tradeoffs"[1] section that calls it an anti-pattern in JavaScript.
In spite of that, there are plenty of reasonable use cases for singletons in many languages, including JavaScript. For example, ES Modules are effectively singletons. If you import the same module in multiple places, it only gets evaluated once.
Let's not turn the singleton pattern into forbidden knowledge.
[1]: https://www.patterns.dev/vanilla/singleton-pattern/#tradeoff...
Why pose DI as replacing singletons when they're used together all the time? Injecting dependencies to create a singleton repository or service class, which is shared across requests.
Singletons are globals and should be treated the same as every other global (that is, used sparingly and with care).
Worse is that singletons enfurece a single instance which is almost always unnecessary. It’s trivial to only create as many instances as you need.
Yes, I have to admit my interest was piqued by the banner, and I then scrolled down, saw the first example was singletons, and closed the tab.
Off the top of my head, rails (currentattributes), Laravel (facades) especially, and most iOS apps use singletons quite well. It’s all in moderation and depends highly on how it’s used, much like every other design pattern.
I think people just don’t like Singletons because they’ve been especially misused in the past but I guarantee the same argument stands for any other design pattern.
Is this JavaScript's take on the GOF book selections plus all the shenans, er "patterns," the ecosystem build tools require?
I was hoping for more high-level architecture based on war stories and experience. This is pretty basic stuff, which has it's value for people earlier in their journey, and does seem to have effort put in from a quick peruse
Most teams don’t fail because they picked the wrong framework; they fail because they never ship enough iterations for it to matter.
Anything that reliably shortens that loop is “good tech,” even if it’s ugly, uncool, or built on last decade’s stack.
Patterns are needed for languages for which the actual underlying concept is unavailable.
For example, prototype pattern is for languages that don't have a way to express interfaces/traits etc as something that can be attached to other language entities.
I was glancing around and landed on the page for the flyweight pattern.[1]
It looks like `addBook` is using the spread operator, which always creates a shallow copy of the book instance properties, thus nullifying any benefits of the flyweight pattern. It also attaches extra arbitrary properties, but still assigns the result to a `book` variable. I don't think this is a great example.
[1]: https://www.patterns.dev/vanilla/flyweight-pattern/
Edit: I forgot to give you kudos for all the effort it must have taken to create all this content, and I appreciate that you're making it available for free.
Good to know I wasn’t the only one thinking “wait a second…” when reading that one and seeing the spread operator being used.
> which always creates a shallow copy of the book instance properties, thus nullifying any benefits of the flyweight pattern
No, the opposite: it highlights the benefits of the flyweight pattern. The shallow copy saves memory. That's the point. You have two identical books. Rather than wasting memory with a deep copy, you make a shallow copy, where all your props point to locations in memory where values are located, and then you modify whatever is different. Now your shallow copy only consumes a small bit of extra memory.
And if those props are all primitives, then you can then modify that shallow copy, and it won't affect the original.
The point is to not make a copy at all for the shared data of the same book. That's even what the page claims is happening (but it's wrong). That's the whole point of the flyweight pattern[1]. Instead, the example returns the same book instance for the same isbn in `createBook`, then blindly copies the shared data like title, author, and isbn every time in `addBook` to a new object.
> The shallow copy saves memory....
Versus not making a copy? A shallow copy of primitives still copies them and uses additional memory. Maybe there's some low-level optimization that makes it more efficient than that, but it's not relevant here. And there isn't any deep cloning happening in the example.
Might as well get rid of the complexity and instantiate a new Book class every time. And maybe stop shallow-copying class instances into new plain objects. It works for the example but has footguns.
Conveniently, there are other patterns on the site that would help you avoid creating an amalgamation of random merged class instances and objects.
The whole example is a mess.
Love this! Just wanted to note that I think there’s a mistake on the flyweight pattern page’s example. You’re using getting a boolean with Set.has but treating it like a Book (as if you had used Set.get). I also don’t really understand how this saves memory if you’re spreading the result into a new object, but maybe someone here can enlighten me!
Ah I think I understand now. The return type of createBook is true | Book, which is likely a mistake, but happens to work because when you attempt to spread a boolean into an object it removes itself. But if you were to edit the example to have a stable return type of Book then it would no longer save memory, so perhaps that was intentional?
Looks more or less like GoF? Maybe compressing files and optimizing 3rd party js files are not patterns.
Great site!
I tend to advocate for people to study design patterns. Not for the purpose that you will necessarily ever use most (or even any) of these exact patterns in your software, but just that you've strengthened your mental muscle for software design in general. I encounter lots of engineers who simply aren't able to think "outside the box" when building something new.
I always wondered if people actually find it beneficial to follow these "design patterns" or not.
Personally, I prefer to learn FP patterns, which tend to be backed with nice mathematical properties behind them.
Too bad the examples are not Typescript, because it's a totally different beast.
a lot of these are misleading, or ungrounded
see the prototype, and observable pattern
they explain the basic concept, but in the only way you would never use it in real life
Looks great. Wish it had a table of contents. Am I missing it?
I hate that singleton is first.
Singletons are just globals with extra steps, and have all the same problems globals have, just people (especially juniors) think they somehow are better.
In reality they’re worse because they conflate global access with enforced single instance. You almost never need to enforce a single instance. If you only want one of something, then create only one. Don’t enforce it unless it’s critical that there’s only one. Loggers are often given as an example of a “good” singleton and yet we often need multiple loggers for things like audit logs, or separating log types.
Instead of singletons, use dependency injection, use context objects, use service locators, or… just use globals and accept that they come with downsides instead of hiding behind the false sense of code quality that is a singleton.
Did this get an update? It's been around for a while.
Are these patterns also the same for mobile apps?
This resource aged surprisingly well. Still one of the clearest ways to understand common frontend patterns.
This looks like an excellent resource for interview preparation. Bookmarked.
Thanks, I was looking for something just like this today!
A singleton for me is just making sure you define a single instance of something at the entry point of your app and passing it down via constructor arguments, which is normally what I do.
I understand you can override modules in tests, and if you have a version of your app that runs in a different environment where you might replace a HTTP service with a different variant (like if an RPC service that normally performs HTTP requests, but in one case maybe you want to talk to specific process, worker or window using message passing).
I really really feel using constructor args is just a lot simpler in most cases. But I think there's a reason why people don't always do this:
1. Sometimes someone is using a framework that imposes a high level of inversion of control where you don't get to control how your dependencies are initialised.
2. (this was me when I was much younger) Someone dogmatically avoided using classes and thought they could get away with just data and functions, and then they realise there is some value in some shared instance of something and then they just undermine any functional purity. Don't get me wrong, functional purity is great, but there are parts of your apps that just aren't going to be functionally pure. And you don't need to go full OOP when you use classes.
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Here are some examples of what I mean.
Here's one example, where I have an app defined in web components and I define the components for each part of the app before passing them into the skeleton. It's a more simple app and I avoid some shared state by different landmark components communicating by events.
https://github.com/AKST/analysis-notebook/blob/b3f082fc63c9b...
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Here's another example, this app is built of multiple command line instructions that sometimes have their own version of services (singletons) with specific configuration, sometimes they are initialised in child processes.
https://github.com/AKST/Aus-Land-Data-ETL/blob/672280a8ded69...
Because this app is doing a lot of scrapeing and I wanted to also child worker processes to do their own HTTP I was going to make a variant of my HTTP service which talked to a daemon process that tracked state for open connections to specific domains to avoid opening too many simultaneously and getting blocked by that host.
Updating the code that uses HTTP will be effortless, because it will continue to conform to the same API. I know this because I've already done this multiple times with HTTP scrapping in the app.
https://github.com/AKST/Aus-Land-Data-ETL/blob/672280a8ded69...
fantastic resource! kindly add svelte design patterns too and sveltekit if you can