用 splice函数分别实现 push、pop、shift、un

实现push方法

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实现pop方法

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实现shift方法

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实现unshift方法

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对以下代码 users中的对象，分别以 name 字段、age 字段、company 字段进行排序

var users = [
{ name: "John", age: 20, company: "Baidu" },
{ name: "Pete", age: 18, company: "Alibaba" },
{ name: "Ann", age: 19, company: "Tecent" }
]

var users = [
  { name: "John", age: 20, company: "Baidu" },
  { name: "Pete", age: 18, company: "Alibaba" },
  { name: "Ann", age: 19, company: "Tecent" }
]
function compare (identify) {
    return function (obj1,obj2) {
        if ( obj1[identify] > obj2[identify])
             return 1;
        else if ( obj1[identify] < obj2[identify])
            return -1;
        else
            return 0;
    }
}
users.sort(compare('age'));
console.log(users)