4.ES6-剩余参数、拓展运算符,以及对象合并的方法(含ES7)

剩余参数

语法：…rest
作用：将参数转成数组传入函数

当我传入指定个数参数时：

function sum(initVal,a,b,c){
    return initVal + a + b + c;
}
sum(10,9,8,7);//34

当我传入不定个数参数时：

function sum(initVal,...rest){
    return rest.reduce(function(val,item,index,origin){
        return val + item;
    },initVal)
}
sum(10,9,8,7);//34
sum(10,9,8,7,6);//40

上例中reduce方法详见：>>传送门<<

拓展运算符

语法:…arr
将数组转成元素列表

let arr0 = [1,2,3];
let arr1 = [4,5,6];
let arr2 = [...arr0,...arr1];//[1,2,3,4,5,6]

如何合并两个对象

方法一：循环遍历

let obj1 = {name:'a',age:18};
let obj2 = {name:'b',gender:'man'};
let obj3 = {};
for(var attr in obj1){
    obj3[attr] = obj1[attr];
}
for(var attr in obj2){
    obj3[attr] = obj2[attr];
}
console.log(obj3);//{name: "b", age: 18, gender: "man"}

方法二：assign

let obj1 = {name:'a',age:18};
let obj2 = {name:'b',gender:'man'};
let obj3 = {};
Object.assign(obj3,obj1,obj2);
console.log(obj3);//{name: "b", age: 18, gender: "man"}

方法三：ES7的对象的拓展运算和ES6的解构赋值

let obj1 = {name:'a',age:18};
let obj2 = {name:'b',gender:'man'};
let obj3 = {...obj1,...obj2};
console.log(obj3);//{name: "b", age: 18, gender: "man"}