我用傳統 js 方法編寫小球動畫時發現三個球球速一個比一個快，而且不能回滾，第三個球一直在原位震動，后來發現是因為我把代碼里的 else { if... else...}當成了 else if.. else...，但我不知道這二者有什么區別，為什么最后動畫結果不一樣？

錯誤代碼：

function?animation(ball,?distance,?cb){
		setTimeout(function(){
			var?marginLeft?=?parseInt(ball.style.marginLeft,?10);
	????	if?(marginLeft?===?distance){
	????		cb?&&?cb();
	????	????}?
	????	else?if?(marginLeft?<?distance){
	????????????marginLeft++;
	????	}?
	????	?????else?{
	????		marginLeft--;
	????	}
	?????????????ball.style.marginLeft?=?marginLeft?+?'px';
	?????????????animation(ball,?distance,?cb);
	????	},?13)
	}

正確代碼：

function?animation(ball,?distance,?cb){
		setTimeout(function(){
			var?marginLeft?=?parseInt(ball.style.marginLeft,?10);
	????	if?(marginLeft?===?distance){
	????		cb?&&?cb();
	????	????}?
	????	else{?if?(marginLeft?<?distance){
	????????????marginLeft++;
	????	}?
	????	?????else?{
	????		marginLeft--;
	????	}
	?????????????ball.style.marginLeft?=?marginLeft?+?'px';
	?????????????animation(ball,?distance,?cb);
	?????????}
	????	},?13)
	}

求解答