caching length

JavaScript performance comparison

Revision 102 of this test case created

Preparation code

 
<script>
Benchmark.prototype.setup = function() {
    'use strict';
    var arr = [];
    for (var i = 0; i < 1000; i++) {
      arr[i] = Math.random();
    }
};
</script>

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Testing in unknown unknown
Test Ops/sec
not cached (basic)
'use strict';
for (let i = 0; i < arr.length; i++) {
  arr[i] *= 2;
}
pending…
cached length
'use strict';
for (let i = 0, len = arr.length; i < len; i++) {
  arr[i] *= 2;
}
pending…
prefix increment
'use strict';
for (let i = 0; i < arr.length; ++i) {
  arr[i] *= 2;
}
pending…
prefix increment + cached length
'use strict';
for (let i = 0, len = arr.length; i < len; ++i) {
  arr[i] *= 2;
}
pending…
decrement
'use strict';
for (let i = arr.length - 1; i > -1; i--) {
  arr[i] *= 2;
}
pending…
decrement without final-expression
'use strict';
for (let i = arr.length; i--;) {
   arr[i] *= 2;
}
pending…
.forEach()
'use strict';
arr.forEach(function(element, i, array) {
 array[i] *= 2;
});
pending…
for in
'use strict';
for(var i in arr) {
  arr[i] *= 2;
}
pending…
.shift() (building new array)
'use strict';
var ar = [];

while (let dee = arr.shift()) {
  ar.push(dee * 2);
}
pending…
while loop
'use strict';
let len = arr.length;
while (len--) {
  arr[len] *= 2;
}
pending…

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