Loops

JavaScript performance comparison

Revision 123 of this test case created

Preparation code

<script>
  var arr = new Array();
  var i = 0;
  while(i < 100) {
    arr.push("x");
    i++;
  }
</script>

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Testing in unknown unknown
Test Ops/sec
while loop that imitates a for loop
var i = 0;
while (i < arr.length) {
 arr[i];
 i++;
};
pending…
while loop that imitates a for loop, caching the length
var i = 0,
    len = arr.length;
while (i < len) {
 arr[i];
 i++;
};
pending…
Reverse while loop
var i = arr.length;
while (i--) {
 arr[i];
};
pending…
Reverse while loop without implicit ToBoolean
var i = arr.length;
while (i-- > 0) {
 arr[i];
};
pending…
Reverse do … while loop
var i = arr.length;
do {
 arr[i];
} while (i--);
pending…
Reverse for loop
for (var i = arr.length; i--;) {
 arr[i];
};
pending…
Old ’n’ busted for loop
for (var i = 0; i < arr.length; ++i) {
 arr[i];
};
pending…
Old ’n’ busted for loop, caching the length
for (var i = 0, len = arr.length; i < len; ++i) {
 arr[i];
};
pending…
Cool guy loop
for (var i = -1; ++i < arr.length;) {
 arr[i];
};
pending…
Cool guy loop, caching the length
for (var i = -1, len = arr.length; ++i < len;) {
 arr[i];
};
pending…
Native Array#forEach implementation
arr.forEach(function(x) {
 x;
});
pending…
Native Array#forEach implementation with named function
function foo(x) {
 x;
};
arr.forEach(foo);
pending…
Loop case 1
var i;
for (i = 0; i < arr.length; i += 1) {
    arr[i];
}
pending…
Loop case 2
var i, l;
for (i = 0, l = arr.length; i < l; i += 1) {
    arr[i];
}
pending…
Stop on undefined
var i = arr.length - 1 
  , o = arr[i];
for (i, o ; o ; o = arr[--i]) {
 o;
}
pending…
for var in loop
for(var i in arr)
{
  arr[i];
}
pending…

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