jquery 操作栈

最近使用前端操作栈记录操作event事件;栈是一种LIFO（Last-In-First-Out）的数据结构，即最先添加到容器中的项目最早被移出。这种数据结构可以限制插入和删除项目。而栈中项的插入和移出只会发生在栈的顶部。stack[]提供push()和pop()方法，用来实现类似栈的行为。
1、先上实例

function Stack() {
    this.stack = [];
    this.actionIndex = 0;
}
Stack.prototype.exec = function (action) {
    action.exec();
    this.stack[this.actionIndex++] = action;
    this.stack.length = this.actionIndex;
    return this;
};
Stack.prototype.redo = function () {
    if (this.canRedo()) {
        this.stack[this.actionIndex++].exec();
    }
    return this;
};
Stack.prototype.undo = function () {
    if (this.canUndo()) {
        this.stack[--this.actionIndex].undo();
    }
};
Stack.prototype.canRedo = function(){
    return this.actionIndex < this.stack.length;
};
Stack.prototype.canUndo = function(){
    return this.actionIndex > 0;
};
function BaseAction(target, newValue,opts){
    this.target = target;
    this.newValue = newValue;
    this.oldValue = this._get();
}
BaseAction.extend = function(setter,getter){
    function Action(){
        BaseAction.apply(this,arguments);   
    }
    Action.prototype = BaseAction.prototype;
    Action.prototype.constructor = Action;
    Action.prototype._set = setter;
    if(getter){
        Action.prototype._get = getter;
    }
    return Action;
};

2、使用事件方法将两个字符串推入到数组的末尾，并将返回的结果保存在变量index中。用index记录栈的存取位置，