Debounce closure

debounce.js

/**
 * Creates a function which fires only once when called in quick succession
 * @param {function...} action the function to fire
 * @param {number} delay amount of time until considered done, default:100ms
 * @param {boolean} asap if should execute at the start of the series (true) or the end (false), default:false
 * return {function} debounced function
 */
var debounce = function(action, delay, asap){
    if ('function' !== typeof action) {
        return null;
    }

    // default to 100ms
    delay = (+delay || 100);//ms

    var timer = 0,
        fire = function(){
            if (timer) {
                clearTimeout(timer);
                timer = 0;
            }

            if (!asap) {
                action();
            }
        };

    return function() {
        if (timer) {
            clearTimeout(timer);
        } else if (asap) {
            action();
        }
        timer = setTimeout(fire, delay);
    };
};