栈的封装

//栈 先进后出
//利用js数组来进行封装
function Stack () {  
    this.items = []
    //入栈
    Stack.prototype.push = function (element) {
        this.items.push(element)
    }
    //出栈
    Stack.prototype.pop = function () {
        this.items.pop()
    }
    //查看栈顶元素
    Stack.prototype.peek = function () {
        return this.items[0]
    }
    //栈内元素的个数
    Stack.prototype.size = function () {
        return this.items.length
    }
    Stack.prototype.isEmpty = function () {
        return this.items.length == 0
    }
    Stack.prototype.toString = function () {
        var str = ‘‘
        for(var i = 0; i < this.items.length; i++) {
            str += this.items[i] + ‘ ‘
        }
        return str
    }
}