ES6 Rest参数与扩展运算符：语法、区别与实战应用

function add(...values) {
 let sum = 0;
 for (var val of values) {
 sum += val;
 }
 return sum;
}

add(1, 2, 3) // 6

// arguments变量的写法
function sortNumbers() {
 return Array.prototype.slice.call(arguments).sort();
}

// rest参数的写法
const sortNumbers = (...numbers) => numbers.sort();

function f(a, ...b, c) { ... } // 报错

(function(a) {}).length // 1
(function(...a) {}).length // 0
(function(a, ...b) {}).length // 1

console.log(...[1, 2, 3]) // 1 2 3

console.log(1, ...[2, 3, 4], 5) //1 2 3 4 5

function push(array, ...items) {
 array.push(...items);
}

function add(x, y) {
 return x + y;
}

var numbers = [4, 38];
add(...numbers) // 42

// ES5 的写法
Math.max.apply(null, [14, 3, 77])

// ES6 的写法
Math.max(...[14, 3, 77])

// 等同于
Math.max(14, 3, 77);

// ES5 的写法
var arr1 = [0, 1, 2];
var arr2 = [3, 4, 5];
Array.prototype.push.apply(arr1, arr2);

// ES6 的写法
var arr1 = [0, 1, 2];
var arr2 = [3, 4, 5];
arr1.push(...arr2);

var arr1 = ['a', 'b'];
var arr2 = ['c'];
var arr3 = ['d', 'e'];

// ES5的合并数组
arr1.concat(arr2, arr3) // [ 'a', 'b', 'c', 'd', 'e' ]

// ES6的合并数组
[...arr1, ...arr2, ...arr3] // [ 'a', 'b', 'c', 'd', 'e' ]

const [first, ...rest] = [1, 2, 3, 4, 5];
first // 1
rest // [2, 3, 4, 5]

const [first, ...rest] = [];
first // undefined
rest // []

const [first, ...rest] = ["foo"];
first // "foo"
rest // []

const [...butLast, last] = [1, 2, 3, 4, 5]; // 报错

const [first, ...middle, last] = [1, 2, 3, 4, 5]; // 报错

var str = 'hello';

// ES5 
var arr1 = str.split(''); // [ "h", "e", "l", "l", "o" ] 

// ES6 
var arr2 = [...str]; // [ "h", "e", "l", "l", "o" ] 

var nodeList = document.querySelectorAll('div');
var array = [...nodeList];