计时器实现

function Timer(id) {
    this.container = document.getElementById(id);
}
 
Timer.prototype = {
    constructor: Timer,
    begin: function(count) {
        var container = this.container;
        setTimeout(function() {
            container.innerHTML = count > 0 ? count-- : "over";
            if(count + 1) {
                setTimeout(arguments.callee, 1000);
            }
        }, 1000);
    }
 
};