ES6(六) 展开运算符

本节知识点

• 展开运算符 … 他只能写在最后面，要是写在前面，后面的参数出不来.
• 这个就是为了方便扩展运算的。

举例

• 老版本

function addNumber(a, b, c, d, e) {
    var numbers = [a, b, c, d, e];
    return numbers.reduce((sum, item) => {
        return sum + item;
    }, 0)
}
console.log(addNumber(1, 2, 3, 4, 5));

• 新版本

function addNumber(...numbers) {
    return numbers.reduce((sum, item) => {
        return sum + item;
    }, 0)
}
console.log(addNumber(1, 2, 3, 4, 5));

对象解析

let expense = {
    type: "es6",
    amount: "45"
};
let a = expense.type;
let b = expense.amount;
console.log(a, b);
const { type, amount } = expense;
console.log(type);
console.log(amount);

• 标准配置

let expense = {
    type: "es6",
    amount: "45"
};
let a = expense.type;
let b = expense.amount;

function fileSammary(obj) {
    return `${obj.type}+${obj.amount}`;
}
console.log(fileSammary(expense));    //结果就是es6+45

• 数组解构

let arr = [1, 2, 3, 4, 5, 6];
const a = [...arr];
console.log(a);