for(var i in array) {

array[i] = ‘whatever’;

}

The difference between i++ and ++i is as follows.

The meaning of i++ is

var temp = i; i = i + 1; return temp;

the meaning of ++i is

i = i + 1; return i;

It’s the creation of that temp that *may* take more time. In JavaScript I suspect most modern browsers can optimize away the need for temp unless you are using it. But ++ comes from C/C++ and in C++ the creation of temp might be some complex type and have side effects.

So, best to just get in the habit of coding what you mean. If you want to increment i then use ++i. If you want to both increment i and get the result before you incremented it than use i++.

You need for(… in …) to iterate through properties of an object though, therefore I’d never advise modifying Array.prototype. E.g:

var a = [];
a["key1"] = “value1″;
a["key2"] = “value2″;

.. if Array.prototype has been modified, it makes things more difficult.

My only concern with Brandon’s example is that if you ~do~ happen to be using a library like jQuery (and that’s a growing percentage of the web populace), that structure can give you problems. I tested it for the purposes of this article and array[i] was returning a function, not the array string I was expecting.

So, if you’re not using jQuery or a similar framework, and never plan to use a JavaScript framework on your pages, by all means go with that system. But if you’re already using jQuery or another framework for something else, you may run into problems!

for() is btw much faster than foreach in php, if the maximum number is given as variable, not as function, thats the problem with foreach, as it always has to check the content of the given array.

so:
$max = count( $array);
for( $i=0; $<$max; $i++){
$array[$i] = 'Do whatever you want to do';
}

is way faster than foreach.

cheers, Frank