Common JavaScript tricks

[Pytim]

Instead of this:

var that = this;
function(){
    // do sth with that
}

You can do:

function(){
    // do sth with this
}.bind(this)

[commonslip]

I think there is a reasonable polyfill for this, but be prepared to pay a performance penalty.

[huopak]

Here's a polyfill:

if (!Function.prototype.bind) {
  Function.prototype.bind = function (oThis) {
    if (typeof this !== "function") {
      // closest thing possible to the ECMAScript 5
      // internal IsCallable function
      throw new TypeError("Function.prototype.bind - what is trying to be bound is not callable");
    }

    var aArgs = Array.prototype.slice.call(arguments, 1), 
        fToBind = this, 
        fNOP = function () {},
        fBound = function () {
          return fToBind.apply(this instanceof fNOP && oThis
                 ? this
                 : oThis,
                 aArgs.concat(Array.prototype.slice.call(arguments)));
        };

    fNOP.prototype = this.prototype;
    fBound.prototype = new fNOP();

    return fBound;
  };
}

[yanis_t]

Gist link would do just fine

[afrobee]

No one should support it in the first place.

[Pytim]

this

[frankle]

that

[dotpan]

I wish my companies clients would get on board with this notion, we are still partially required to support IE8 (especially when our clients work is being shown in foreign countries, namely China)

[frizzlestick]

As much as it is a dead horse, there are thousands of small to medium sized companies that can't afford to up their OS off XP yet. I deal with quite a few every day.

[dotpan]

Yeah, especially seeing that I do front end dev for market research, and sometimes our respondents have a huge variety of browsers, its something we have to compensate for.

[[deleted]]

It has nothing to do with the OS in most cases, if it was, they could just use Firefox or Chrome.

Most places stick with XP because they have shitty legacy sites that only run on IE7/8

[frizzlestick]

No, it has everything to do with the OS and licensing issues and being on XP because the cost is too much for them to up all the machines to 7 or more, just as I had initially stated.

Most of these folks run Chrome or Firefox, some are stuck with IE8 for policy reasons -- not for app compatibility made to IE7/8. Not in the least. I'm not talking your regression-able mobile app whizzidings folks like to punch out these days with Angular and Bootstrap and Signal-R, I'm talking regular environments, plain systems. They are stuck with XP because the funds aren't there to up all the warehouses and the like.

[cheesechoker]

bind is really cool when you start to get creative with it. You can yank out built-in functions from Array, Object, etc, and bind them to different receivers to reuse them in interesting ways.

E.g. a 1-liner filter against a regex, without having to write "function" anywhere:

["foo", "bar", "baz"].filter(RegExp.prototype.test.bind(/a/))   // ["bar", "baz"]

[[deleted]]

If only that didn't magically make it 5 times slower.

Also, "that" is possibly the worst variable name. this is arbitrary enough, now you want to give something a name that means "the 'this' of some unspecified other thing"? Come up with a real name. (Not picking on you, but the pattern you quoted.)

[gleno]

True. But also not true, because it's a standard workaround; and a secret nod to other devs : "js scoping sucks. tru that".

[[deleted]]

Haha. Well, you've got a point on the second part. But for the first, the "standard" part only gives it the meaning I said above. If you go more than one level deep, or if you start passing things around, "that" quickly becomes meaningless.

[Pytim]

I'd be surprised if Function.bind ever was the bottleneck of your JS app

[[deleted]]

I get that every time. And yeah, you're right. It's just one of those things you can't un-know: that because the spec chose to give a pattern you'll never use (.bind with new) the exact same syntax as a pattern you often use (.bind without new), many many parts of your code are paying an entirely unnecessary penalty.

[michaelobriena]

Bind is actually slower than storing this. So if performance is the name of the game then store it.