But know i see that it seem most logical, no ?
browsers.forEach(function(item) { alert(item); });

For instance, guess what this displays:
var i = 50;
for( var i = 0; i< 10; i++ ) {}
alert(i);

Every time you use a for loop and define a loop variable, that variable is scoped to the containing function, not the loop block.

I miss perl-style map and foreach every time I write a loop in Javascript.

Patrick


var a = [ 1, 2, 3 ];
for (var i = 0, len = a.length; i < len; i++) {
// work
}


Also, though I haven’t benchmarked it, when order of traversal isn’t important, I typically prefer fewer locals and opt instead of constant comparison.


for (var i = a.length - 1; i >= 0; i--) {
// work
}


Correct me if I am wrong.

var length = arr.length
for(var i=0;i<length;i++){
// code here
}

Based off olliej’s test, its one of the faster ones. I was certainly surprised to see that recalculating the arr length through each iteration was so costly, but it makes sense in that it adds at best a constant or at worst a linear operation to an already linear process.

You really only need to worry about loop performance if you are dealing with large arrays though, which most javascript applications I develop don’t use.

@RyanMorr: Actually Array.prototype.forEach (and most other array prototype functions) are defined as being generic, the mozilla MDC documentation gives JS implementations as well and there’s no type checking, basically they’re all

var l = this.length;
for(i = 0;i i<l; i++) { … }

Array.forEach(arguments, function(){
//do something
}, scope)

I find it the most useful method for array iterations.

Here are a few more that are a lot quicker

nopIteration0 : 22ms
function nopIteration0(a, f) {
var start = new Date;
var i = a.length;
while(i--) {
}
var end = new Date;
return end - start;
}

nopIteration1 : 38ms
function nopIteration1(a, f) {
var start = new Date;
var l = a.length;
for (var i = 0; i < l; i++){
}
var end = new Date;
return end - start;
}


Some benchmarks please.