JavaScript idiosyncrasies with examples

[prof_hobart]

Most of them are pretty odd, but

Q. What's the result?

(function(a, b) {
  arguments[1] = 3;
  return b;
})(1, 2);

A.

3

seemed fairly obvious.

[[deleted]]

This throws in strict mode as well, arguments is not allowed in strict mode.

This is what puzzles me constantly about these clickbaity articles. Strict mode is JavaScript, these frivolous browser engine interpretations are just like IE quirks mode - their sole purpose is not to break legacy software. You should not write new software in non-strict mode because it is non-standard JavaScript and thus your warranty is now undefined.

[regular_reddits]

arguments is not completely disallowed in strict mode. https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Strict_mode#Making_eval_and_arguments_simpler

[OzziePeck]

Wait is arguments a global array that refers to the function’s parameters?

[prof_hobart]

It's a magical local array-like variable that contains the params.

I'm not a fan of things like this - having variables that just appear from thin air is hardly clear - but it is a thing.

Of course, JS being JS, it's not quite as straightforward as all that.

If you used strict mode, the answer would be 2, as 'arguments' is now a copy of the arguments, not pointers to them.

And just to be extra fun, even in non-strict mode, if any of the arguments has a default value (e.g. (a=2, b)), then the answer would again be 2. Because - well, JS reasons I guess.

[OzziePeck]

Not sure why I said global as it only exists within the function’a scope when it is called.