I've noticed this code snippet used in various places:
for (var i = 0, len = myArray.length; i < len; i++) {
}
I understand that this is caching the length of the array.
Recently, I encountered this alternative approach:
var len = myArray.length; var i = 0; while(i++ < len)
In terms of efficiency, both methods should be equal, correct? Any insights would be welcomed.
If you find yourself in a typical loop situation, consider switching from using i < len to i !== len. This small change can greatly improve the speed of the loop execution, as checking for inequality is a quick operation. While caching the variable may not be essential, it certainly won't hurt.
To create a speedy loop in JavaScript, use the following structure:
for (var i = 0, len = myArray.length; i !== len; i++) {
}
UPDATE
In the past, I conducted some performance tests that led me to this conclusion. However, recent browser behavior has shifted, with the opposite now being true (< is faster than !==). To see for yourself, check out this test I just ran: http://jsperf.com/loop-inequality-check
It seems my earlier recommendation is no longer valid ;)
Create a jsperf test scenario here:
http://jsperf.com/javascript-array-length
for (i = 0; i < arr.length; i++) {
//no action
}
var arrlength = arr.length;
for (i = 0; i < arrlength; i++) {
//no action
}
var arrlength = arr.length,
i = 0;
while (arrlength > i++) {
//no action
}
var arrlength = arr.length;
while (arrlength--) {
//no action
}
If there are suggestions for enhancing the test cases, do inform me in the comments section. Based on limited tests, it appears that IE11 is more optimized for the while scenarios with a few iterations, while Chrome 31 seems to favor the second for loop (which is quite similar to the while).
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