`in` keyword compiles to unnecessarily awkward js...

[torvalamo]

Unless I'm missing something,

if a in array
unless a in array

should simply compile to

if (~array.indexOf(a))
if (!~array.indexOf(a))

rather than the incredibly contrived

var __indexOf = [].indexOf || function(item) { for (var i = 0, l = this.length; i < l; i++) { if (i in this && this[i] === item) return i; } return -1; };

if (__indexOf.call(array, a) >= 0)
if (__indexOf.call(array, a) < 0)

What ancient browser are you trying to support that doesn't have indexOf on arrays? At the very least learn what the tilde operator does ;)

[brian-c]

IEs < 9 don't have Array::indexOf.

[torvalamo]

OH really... my bad. Still. Tilde. :P

[epidemian]

I personally prefer >= 0 to ~, as it's quite more obvious IMO.

[jashkenas]

Yep -- >= 0 is for readability.

[Soviut]

I'd have to agree, this is the first time I'd heard of the tilde "bitwise not operator" in Javascript. That doesn't make it "wrong" but it certainly is a lot harder to read aloud than "if the index of this item in this array is greater than or equal to zero".

[GeoffreyBooth]

Is >= 0 more readable than !== -1? My habit has been to always write !== -1, thinking that it must be faster for the runtime to evaluate a boolean than >=, but apparently Chrome, at least, is smart enough to treat them identically. So I guess it comes down to readability; I guess people find it more readable to check for a positive condition (>=) rather than the absence of a negative one (!==)?