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Call, bind and apply should be discarded and forgotten about, they add too much confusion, there are better ways, and they end up being used as terrible intervi

• kecupochren 5y ago
  I've literally never used them during my 8 years of working as a JS dev. Maybe I'm doing it wrong. Edit: actually I did use .bind with React before arrow functions came
  • hajile 5y ago
    Until for..of came around, `Array.prototype.map.call($nodeList, myFn)` was pretty much the way to iterate over things that were "array-like" but didn't actually inherit from Array, so didn't have such methods.
  • nicoburns 5y ago
    They were pretty widely used (especially in library code) before arrow functions were added to the language.
• jenseng 5y ago
  You get "clean and DRY" at the expense of "not beginner-friendly" and "you need be to very careful". Thanks, but no thanks. I'll take clear, understandable code over clever footguns any day.
• user3939382 5y ago
  I figure there’s 3 possibilities: I’m just dumb, I don’t use it enough, or JavaScript is poorly designed. For some reason, even after 20 years of using JavaScript on and off and reading a dozen books about it, I can’t articulate exactly how the language works, how scope is evaluated, the composition of objects and prototypes which has some kind of turtles-all-the-way-down thing going on with it. When I read explanations in books it’s like hmm ok.. I guess that makes sense. Then a week later I don’t remember. The languages I’ve spent the most time with are SQL, PHP, Bash, and Clojure, and I never felt that way about them. Maybe it’s just me.
  • nicoburns 5y ago
    Prototypes are quite simple. An object may have a prototype. If it does then that prototype is just another object, which is considered the first objects parent (which works with method calls like class based inheritance). The chain ends because it's also possible for an object not to have a prototype.
  • wruza 5y ago
    I also had this trouble, because for all other languages you can just tead the spec once and that’s it. But ES specs are too technical to be used as such. After few years I just read non-boring parts of ES6 and it cleared all dark corners. I’d say all of the articles on the internet are rehashing the spec in (at best) a dubious and ritualistic way, and have zero technical value if you ask me.
  • bluepnume 5y ago
    My advice is to start of with javascript by forgetting 100% about classes, inheritance, prototypes, and so on. Just use vanilla functions and objects, and when in need of something that looks like a class, reach for the revealing module pattern: https://gist.github.com/zcaceres/bb0eec99c02dda6aac0e041d0d4d7bf2 https://gist.github.com/zcaceres/bb0eec99c02dda6aac0e041d0d4...
    • rustyminnow 5y ago
      I've used this pattern before, but run into issues when you want to write tests for "private" functions (like loadSong() in this example). What I've done is name them like _loadSong and expose them anyways, but that doesn't feel great. Is there a better way?
      • moron4hire 5y ago
        You don't write tests for private methods.
        • exdsq 5y ago
• normac2 5y ago
  > Incidentally, we should also discard `this`, unless directly inside a class method. When you say it has to be "directly," do you mean we should never use arrow functions (or use them only for looks)? Since the purpose of those is to add "this" support to inner functions?
  • bluepnume 5y ago
    Sorry, yeah, I did allow for closures inside class methods with that statement. That's fine by me.
• cj 5y ago
  > should be discarded and forgotten about, they add too much confusion How does it add confusion? Bind, call and apply are fairly straightforward and not difficult concepts to grasp for any mid to advanced level JS dev and they're useful in many scenarios (although bind is less useful / less needed now that we have arrow functions, but call and apply are definitely not something to be "discarded").
  • Arnavion 5y ago
    `call` and `apply` can also be replaced with arrow functions and splats.
    • hajile 5y ago
      How would you replace the classic `Array.prototype.map.call($nodeList, myFn)` with arrows and splat?
      • nicoburns 5y ago
        You could do it like this: const mapNodeList = (...nodeList) => nodeList.map(myFn); mapNodeList(...$nodeList)
        • hajile 5y ago
          That creates an entire extra list of garbage.
          • chrisseaton 5y ago
            Doesn’t the compiler optimise it away?
            • hajile 5y ago
              Those aren't the same types. One is a DOM array and the other is a JS array. They don't share the same constructor or the same prototype chain.
• ubaltaci 5y ago
  that list should also include anything that touches prototypes
  • bluepnume 5y ago
    You have my full agreement. You can write great javascript without ever touching prototypes, and probably even avoiding inheritance altogether unless you have a really succinct use-case.
• hajile 5y ago
  There is literally NO substitute for either call or apply as they are low-level JS primitives. Arrow functions can go a long way toward handling .bind() scenarios, but I believe there are situations where you must still use .bind() to prevent constantly creating new functions (and the related garbage).
  • bluepnume 5y ago
    Show me some code you can only write using either call, apply, or bind.
    • wruza 5y ago
      Anything that substitutes ‘this’ but doesn’t want to put a function into that object. const {filter} = [] class Foo { less() { return filter.call(this, sometest) } } There is no way to closure it somehow without (temporarily) modifying an instance of Foo. (The next obvious question is “why” and the answer is “metaprogramming”.)
      • bluepnume 5y ago
        I would rather re-implement `filter` in a way that is specific to `Foo`, than to attempt to use an array method on my class.
  • wruza 5y ago
    .bind() does create a new function, though it has far less “slots” than a regular one. It doesn’t modify the original function. The spec doesn’t specify anything beyond that, afair, and if binds aren’t cached in some way (easy to check with === or roll up your own cachedBind()), GC barely can make any benefit out of collecting slightly smaller objects (but the interpreted part of a runtime may still process bound functions a little faster than closures doing the same thing). As of source code or p-code or by whatever structure {<code>} body is represented inside, it is always* static for all closures, so there is no overhead apart from a closure itself between: function foo() {<code>} // func for (;;) foo() and let i = 0 for (;;) { let j = 0 function foo() {i++; j++; <code>} // closure foo() } Because {…<code>} is a singleton in both snippets. * of course jit may blur this distinction a lot, but that’s unrelated
• jollybean 5y ago
  I came here to write exactly that. There was once a time when such 'js ninja' skills were appropriate, but now they almost represent an anti-pattern in normal usage. For some kind of framework, maybe. But otherwise, they're just going to cause problems and they don't really provide something really valuable wherein another more basic use case wouldn't be better. A pragmatic approach might be to 'stick to a solid version of Typescript' and even then be wary of the fancy stuff unless it's truly needed. (Say, you're building a lib or some core module).
• wruza 5y ago
  Sadly (or not, really) there are no class/instance methods in javascript, cause its key lookup model is prototype-based and ‘method’ functions just get ‘this’ lexically (in x.y.f(), f() operates on x.y). The combination of these two facts builds up an entire OOP in js. If you really want to free your code of these ideas, it’s much easier to use some js-transpilable language out there.
  • bluepnume 5y ago
    > in x.y.f(), f() operates on x.y Yep, and I think that determining `this` at the call-site is really awful, and has been the cause of many more bugs than is reasonable. OOP you can do in JS with just `class` and `extends`, you no longer need to care too much about prototypes and how they work. Prototypes have become much more of an implementation detail in recent years.
    • wruza 5y ago
      I think that determining `this` at the call-site is really awful, and has been the cause of many more bugs than is reasonable That’s what almost all (more or less) dynamic languages do, except those that don’t have an arbitrary “object” struct. Out of few dynamic languages only python does what you need, at the cost of the enormous GC pressure. It’s okay for python because it was meant to be slow as hell by design. And even then the solution would be more error-prone than the “issue” itself. Consider this code: app.use(sass({ src: “.”, log: console.log, log2: function () {…}, })) Should the anonymous object overtake console.log()’s “this”? And for log2()? And if you create an object and assign a bunch of functions to it in a literal? Later in the code? Your frustration is understandable, but I assure you that python’s “bound methods” are really awful to debug as well (been there done that), because the issue is not in functions taking “this” one way or another, but in a mismatch between developer’s expectations and reality.
      • bluepnume 5y ago
        I agree with you, it's definitely a trade-off between developer ease and perf. I get around that in js mostly by avoiding classes and `this` entirely unless I'm sure I'm going to have a large number of instances of something. But there is the mental overhead of "Do I need to wrap this function in an arrow function before passing it around to avoid getting an unexpected `this`?" So yeah, not saying I have a great solution -- just that none of the existing solutions really seem ideal.
• JoeCortopassi 5y ago
  Every language has parts that are harder to understand because they unlock the deep magic. If you really haven't found a use case for call/apply/bind, or are confused by `this`, it's more likely that your focus has been on thin-client user facing applications for most of your career. These language features are invaluable for tool building, and are foundational to most of the tools you probably leverage to make thin-client user facing apps NOTE: most developers work in thin-client user facing applications, that's not a dig or anything, it's just where 99% of the work exists
  • bluepnume 5y ago
    I've worked full-stack in javascript for many years, and I've written plenty of libraries and tooling. I've used call/apply/bind/this extensively and I understand them to a fault. I would still remove them in favor of arrow functions and spreads. Unless you can show me any code which is pivotal to writing some tool which absolutely can not be done using the alternatives.
    • JoeCortopassi 5y ago
      `Array.prototype.slice.call(arguments)` is a good example. In fact, I'm struggling to think why you would replace anything other than bind with an arrow function EDIT: My example is bad, you could just `[...arguments]`
      • bluepnume 5y ago
        `Array.prototype.slice.call(arguments)` can be replaced with `Array.from(arguments)` (or as you mentioned `[ ...arguments ]`)
    • asiachick 5y ago
      arrow functions and spread do not cover all use cases of call/apply/bind proxies and wrappers are two areas where you need call because you need be able able to pass the correct "this" which arrow functions will fail to do
    • 5y ago
• Sephr 5y ago
  I've had to cache a secure reference to call() in a JS library intended to exist in potentially hostile environments. This call helper is often used to avoid prototype pollution vulnerabilities when patching native prototypes.
  • bluepnume 5y ago
    Very interested to learn more about this use case. This is to protect against hostile environments blocking function calls by polluting prototypes? I do a lot of work on SDKs which run in semi-hostile environments, so prototype pollution is something I'm frequently running up against.
    • Sephr 5y ago
      > This is to protect against hostile environments blocking function calls by polluting prototypes? Correct. I go into more detail about into our problem space and use cases here: https://transcend.io/blog/defeating-cookie-banners https://transcend.io/blog/defeating-cookie-banners
• arcosdev 5y ago
  We shouldn't use 'class' either
• Tade0 5y ago
  How do you want to do partial application if not through bind? All the other methods are much more verbose.
• matheusmoreira 5y ago
  > Incidentally, we should also discard `this`, unless directly inside an instance method of a class. We should discard classes instead. People have trouble understanding `this` because they insist on thinking in terms of classes and methods which are second class concepts in Javascript. Once I understood objects and prototypes, `this` also became easy to understand. Programming with Object.create produced the cleanest code I've ever seen. Nothing but functions, objects and prototypes. I simply don't understand why the new versions of Javascript insist on adding even more of this class stuff.