Javascript instant iterators

Today’s useful Javascript snippet:

function iterate( iterable ) {
    var i = -1;
    var iterator = function() { return i < 0 ? null : i < iterable.length ? iterable[ i ] : null; };
    iterator.next = function() { return ( i + 1 ) < iterable.length ? iterable[ ++i ] : null; };
    return iterator;
}

As a Perl-spoiled brat, I find myself using this or a slight variation on it pretty often. It enables me to write the following:

for( var sheet = iterate( document.styleSheets ); sheet.next(); ) {
    if( sheet().href ) {
        do_something( sheet() );
    }
}

rather than the far more tedious and annoyingly repetitive:

for( var i = 0; i < document.styleSheets.length; ++i ) {
    var sheet = document.styleSheets[ i ];
    if( sheet.href ) {
        do_something( sheet );
    }
}

to say nothing of:

for( var i = 0; i < document.styleSheets.length; ++i ) {
    if( document.styleSheets[ i ].href ) {
        do_something( document.styleSheets[ i ] );
    }
}

And of course these are just silly examples. In real code, where you often want to nest several loops, the repetition gets hideous real quick like.

References to this article: Javascript instant iterators, refined.