Using length magic function is bad

JavaScript performance comparison

Test case created by Dan Andreescu

Preparation code

 
<script>
Benchmark.prototype.setup = function() {
    var a = [1,2,3,4,5,6,7,8,9,0,123,12,1,41,24,124,124,124,1245,13,52,35,233,5,2345,34,63,46,36,34,63,46,346,3,763,7,3457,35,234,35,57,35,3346,36,3,63,4,4,6,8,4,8456,84,5,3,612,36,347,3,734,57,457,45,735,74,57,47,3,46];
    var len = a.length;
};
</script>

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Testing in unknown unknown
Test Ops/sec
using length in the for loop
for (i = 0; i < a.length; i++) {
    var k = a[i];
}
pending…
caching length before the loop
for (i = 0; i < len; i++) {
    var k = a[i];
}
pending…

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