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polyfill an ES5-compatible Array.prototype.indexOf

Polyfill for ES5: Array.prototype.indexOf

A tweet-sized ES5-compatible polyfill for Array.prototype.indexOf

// Avoid overwriting prototype if not neccessary
[].indexOf||(Array.prototype.indexOf=
function(
a, // search item
b, // startIndex and/or counter
c // length placeholder
) {
for (
// initialize length
var c = this.length,
// initialize counter (allow for negative startIndex)
b = (c + ~~b) % c
// loop if index is smaller than length,
// index is set in (possibly sparse) array
// and item at index is not identical to the searched one
b < c && (!(b in this || this[b] !== a));
// increment counter
b++
);
// if counter equals length (not found), return -1, otherwise counter
return b ^ c ? b : -1;
})
[].indexOf||(Array.prototype.indexOf=function(a,b,c){for(c=this.length,b=(c+~~b)%c;b<c&&(!(b in this)||this[b]!==a);b++);return b^c?b:-1;})
DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE
Version 2, December 2004
Copyright (C) 2011 Alex Kloss <alexthkloss@web.de>
Everyone is permitted to copy and distribute verbatim or modified
copies of this license document, and changing it is allowed as long
as the name is changed.
DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE
TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
0. You just DO WHAT THE FUCK YOU WANT TO.
{
"name": "indexOf",
"description": "polyfill an ES5-compatibile Array.prototype.indexOf where needed.",
"keywords": [
"array",
"indexof",
"es5",
"polyfill"
]
}
<!DOCTYPE html>
<title>Foo</title>
<div>Expected value: <b>0,1,2,-1</b></div>
<div>Actual value: <b id="ret"></b></div>
<script>
var indexOf =
[].indexOf||(Array.prototype.indexOf=function(a,b,c){for(var b=b|0,c=this.length;b<c&&(!(b in this||this[b]!==a));b++);return b^c?-1:b;})
var testdata=[1,2,3,5];
document.getElementById( "ret" ).innerHTML = [indexOf.call(testdata,1), indexOf.call(testdata,2), indexOf.call(testdata,3), indexOf.call(testdata,4)];
</script>
@Kambfhase

To be fully ES5-compatible you need to iterate from left to right:

 [1,1,1].indexOf(1) // 0, ES5
 (function(a,b,c){for(b=this,c=b.length;b[--c]!==a&&~c;);return c}).call([1,1,1],1) // 2, yours
@atk
Owner
atk commented Jun 19, 2011

I knew it was too easy. Standby for corrected version :-)

@Kambfhase

while you're at it, also try implementing the optional fromIndex.

@atk
Owner
atk commented Jun 19, 2011

One at a time, my friend. Always one at a time :-) Corrected version is up.

@atk
Owner
atk commented Jun 19, 2011

Though my last version could dub as lastIndexOf :-)

@atk
Owner
atk commented Jun 19, 2011

@kambfhase : If I get it right, fromIndex is another argument limiting the start/end of these methods?

@jney
jney commented Jun 27, 2011

yes, fromIndex specify the beginning of the search : https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Array/indexOf#section_3

something like this should work :

Array.prototype.indexOf=function(a,f){for(var c=this.length,r=-1,d=f>>>0;~(c-d);r=this[--c]===a?c:r);return r}
@atk
Owner
atk commented Jun 28, 2011

Thanks. I shortened this a bit, though.

@jed
jed commented Jul 11, 2011

sorry @atk, this package.json is invalid too, because of the trailing keywords comma.

@jdalton
jdalton commented Aug 21, 2011

Despite the description, polyfill an ES5-compatible Array.prototype.indexOf, this is not an ES5 compatible fallback because it lacks sparse array support and resolves the length incorrectly. Also browsers like Chrome have a bug where Array.prototype.indexOf = [].indexOf will cause Array#indexOf to become enumerable.

@phoetry
phoetry commented Dec 5, 2011

Hi @atk
In the first version(with startIndex), you should move the ++increment to the repeatingExpression.
Try [1,2].indexOf(1).

@atk
Owner
atk commented Dec 5, 2011

This should be better :-)

@jdalton
jdalton commented Dec 5, 2011

This doesn't handle negative fromIndex's correctly.

@atk
Owner
atk commented Dec 5, 2011

Thanks, I'm working on it.

Update: works now.

@jdalton
jdalton commented Dec 6, 2011

Doesn't handle when the negative fromIndex plus the length result in less than 0;
See step 8b

@ryansully

annotated.js line 16 has incorrect parentheses:

b < c && (!(b in this || this[b] !== a));

should be:

b < c && (!(b in this) || this[b] !== a);
@bergus
bergus commented Jun 4, 2013

This polyfill function has the wrong arity. The spec states:

The length property of the indexOf method is 1.

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