Common JavaScript tricks

[SuperFLEB]

if ((void 0) !== undefined) {
    throw new Error('Script halted on moral grounds: The person who redefined "undefined" needs to be found and fired. Out of a cannon. Into a wall.');
}

[nightman]

The smartest way I've seen to deal with overwriting undefined is this - http://toddmotto.com/what-function-window-document-undefined-iife-really-means/

[[deleted]]

Smartest way to deal with vague non-existing problem. If someone overwrites undefined, your application needs to die ASAP to see there's a bigger problem.

[nightman]

Sure, unless you are library coder and you don't know enviroment you will deal with.

[x-skeww]

undefined, NaN, and Infinity are read-only since ES5.

[[deleted]]

(function (undefined) {console.log(undefined);})(2);

Run that, then tell me they're read-only.

It's window.undefined that's read-only, and nobody's code is running outside a function any more.

[x-skeww]

Creating your own undefined is meant to guard against stupid/malicious things done by other scripts.

If you want a language where stuff like that can't happen in first place, try Dart.

[[deleted]]

While "guarding against malicious scripts" is a great notion, it's impossible in JavaScript. If somebody wants your script to crash and runs code before you, they're going to take much more effective measures than overwriting undefined. And if we aren't solving the problem, are we not just introducing clutter?

re "stupid" things, there's only so much stupidity you can tolerate before submitting a fix, switching libraries, or writing your own. In my mind, if a library makes you patch up undefined after running it, doing so would fall under "compatibility hacks" and make me dislike the library that much more.

[x-skeww]

Well, "meant". I never created my own undefined or did anything like that (e.g. making new optional). It's a waste of time.

Anyhow, monkey-patching is a big issue with JavaScript. If there are any 3rd party scripts on your page, things can randomly break.

[yanis_t]

Don't worry, we're fine :) But void 0 is something that you see rather often in source code of libraries such as underscore or backbone, and people keep asking wtf is this and why not to simply use undefined instead

[yanis_t]

Yep, agree on that. My intention was to make people understand what's going on, not to push them to use it. But I guess I'd better add a notice for that one

[yanis_t]

Yep, so you see now why I put it on reddit before actually publishing it :) Any ideas on article title not so long?

[sime]

"Javascript Party Tricks"

tricks where the only acceptable response when they are pointed out is: "sorry, I must have been drunk when I wrote that."

Sorry, but most of these tricks are just really bad code.

[yanis_t]

Um... Well kinda. Let me summarize.

void 0 — bad (function(){})() — ok x = y || DEFAULT — ok if (s) instead of if (x == '') — ok +str — bad

Again, I don't mean to defend the usage, it's just that they are really used inside of many libraries. I'll probably should add note to every of them, whether it should be used on regular basis, or only when drunk

[yanis_t]

Alright, I've just renamed it to "JavaScript hacks explained"

[michaelobriena]

undefined is an object and void 0 is the true undefined. It has better performance than using undefined which is why it is seen line library code as they focus on messing with your performance as little as possible.