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polyfill an ES5-compatible Array.prototype.indexOf

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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.
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Polyfill for ES5: Array.prototype.indexOf

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

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// 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;
})
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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;})
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{
"name": "indexOf",
 
"description": "polyfill an ES5-compatibile Array.prototype.indexOf where needed.",
 
"keywords": [
"array",
"indexof",
"es5",
"polyfill"
]
}
View LICENSE.txt
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<!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>

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
Owner
atk commented

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

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

Owner
atk commented

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

Owner
atk commented

Though my last version could dub as lastIndexOf :-)

Owner
atk commented

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

jney commented

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}
Owner
atk commented

Thanks. I shortened this a bit, though.

jed commented

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

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.

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

Owner

This should be better :-)

This doesn't handle negative fromIndex's correctly.

Owner

Thanks, I'm working on it.

Update: works now.

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

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 commented

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

The length property of the indexOf method is 1.

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