用法1：替换数组的值

let a = [1,2,3],b = [4,5]
console.log( Object.assign(a,b)); // 后面的值覆盖前面的值,[4,5,3]


用法2：为对象添加属性
下面是es5的写法：this.xxx =xxx

  //    es5的写法
       class Test{
            constructor(x,y){
                this.x =x
                this.y = y
            }

            sum(){
                return this.x +　this.y
            }
       }
       let t = new Test(1,2)
       console.log(t.sum());



用Object.assign的写法

       // Object.assign的写法
       class Test2{
           constructor(x,y){
             Object.assign(this,{x,y})
           }
           sum2(){
               
               return this.x + this.y
           }
       }

       let t2 = new Test2(1,2)
       console.log(t2.sum2());



用法3 深度克隆对象

//    用法3 深度克隆对象
     let clone = (orignObj) => {
            let originProto = Object.getPrototypeOf(orignObj)
            return Object.assign(Object.create(originProto), orignObj)
        }
        let obj3 = { name: 'zs', age: 12 }
        console.log(clone(obj3));



用法4：合并对象属性
下面这种写法，合并后，原来的两个对象都已经改变
// example1
        let obj = {name:'zs'} ,obj2 = {name:'zs',age:12}
        let merge = (target, ...v) => Object.assign(target, ...v)
        console.log(merge(obj,obj2));// {name:'zs',age:12}
        console.log(obj,obj2); // 合并后，两个对象都已经改变，值都是 {name:'zs',age:12}
如果不想改变原来的对象，可以用下面这个写法

  // example2 合并后，返回一个新对象，不更改原有对象的属性
        let merge2 = (...v) => Object.assign({}, ...v)
        console.log(merge2(obj, obj2));// {name:'zs',age:12}
        console.log(obj); //  原来的对象保持原样  {name:'zs'}
        console.log(obj2); //  原来的对象保持原样  {name:'zs',age:12}

//合并对象，还可以用展开操作符
let obj5 = {name:'zs'},obj6 = {age:12}
let newOjb = {...obj5,...obj6}
console.log(newOjb);

       
用法5.为默认对象新增属性

const DEFAULTS = { name: 'zs', age: 13 } // 默认对象
let createObjWithDefault = (opt) => Object.assign({}, DEFAULTS, opt)
console.log(createObjWithDefault({ 'addr': 'gz' }));