For Loop vs. Optimized For Loop

JavaScript performance comparison

Revision 8 of this test case created by Jônatas Pedraza

Info

A speed comparison between for loops.

Preparation code

<a href="#">Test</a>
<a href="#">Test</a>
<a href="#">Test</a>
<a href="#">Test</a>
<a href="#">Test</a>
<a href="#">Test</a>
<a href="#">Test</a>
<a href="#">Test</a>
<a href="#">Test</a>
<a href="#">Test</a>

Preparation code output

Test runner

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Testing in unknown unknown
Test Ops/sec
Customary For Loop
var anchors = document.getElementsByTagName("a");

for (var i = 0; i < anchors.length; i++) {
  anchors[i].style.color = "red";
}
pending…
Optimized For Loop
var anchors = document.getElementsByTagName("a");

for (var i = anchors.length - 1; i >= 0; i -= 1) {
  anchors[i].style.color = "red";
}
pending…
for in loop
var anchors = document.getElementsByTagName("a");

for (var x in anchors) {
  anchors[x].style.color = "red";
}
pending…
length caching
var anchors = document.getElementsByTagName("a");

for (var i = 0, length = anchors.length; i < length; i++) {
  anchors[i].style.color = "red";
}
pending…

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