throttle.js

function throttle ( fn, threshhold, scope ) {
    threshhold || (threshhold = 250);
    var last,
        deferTimer;
        
    return function () {
        var context = scope || this;

        var now = +new Date,
            args = arguments;
            
        if ( last && now < last + threshhold ) {
            // hold on to it
            clearTimeout(deferTimer);
            deferTimer = setTimeout( function () {
                last = now;
                fn.apply( context, args );
            }, threshhold );
        } else {
            last = now;
            fn.apply(context, args);
        }
    };
}