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.

Referenced in Javascript instant iterators, refined.