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Created June 19, 2011 15:45
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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>
@ryansully
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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
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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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