共计 2591 个字符，预计需要花费 7 分钟才能阅读完成。
ES6+ 好用的小技巧，让你的代码更干净，短巧，易读
模板字符串
let name = ‘siri’, age = 18, job = ‘front-end engineer’
let oldStr = ‘Hi, ‘ + name + ‘, I\’m ‘ + age + ‘ and work as a ‘ + job + ‘.’;
let newStr = `Hi, ${name}, I’m ${age} and work as a ${job}.`;
扩展操作符
… 操作符，有两个主要用处：
复制一个新的数组或对象
把多个参数赋值给一个数组变量
把一个数组变量赋值给多个参数
let a = [1, 2, 3]
let b = […a] // b 是一个新的数组，内容和 a 一样
let c = […a, 4, 5, 6]
let car = {type: ‘vehicle ‘, wheels: 4};
let newCar = {…car}
console.log(newCar); // {type: ‘vehicle ‘, wheels: 4}
// 合并对象属性，后边的属性会覆盖前边的，可用于修改对象的某个属性值
let car2 = {…car, type: ‘vehicle2’, wheels: 2} // {type: “vehicle2”, wheels: 2}
function foo(…args) {
console.log(args);
}
foo(‘car’, 54, ‘tree’); // console.log 输出 [‘car’, 54, ‘tree’]
默认参数
// 给方法添加默认参数值
function foo(a = 5, b = 10) {
console.log(a + b);
}
foo(); // 15
foo(7, 12); // 19
foo(undefined, 8); // 13
foo(8); // 18
foo(null); // 10 as null is coerced to 0
// 默认参数值也可以是表达式或者函数
function foo(a) {return a * 4;}
// y = x + 4, z = foo(x)
function bar(x = 2, y = x + 4, z = foo(x)) {
console.log([x, y, z]);
}
bar(); // [ 2, 6, 8]
bar(1, 2, 3); //[1, 2, 3]
bar(10, undefined, 3); // [10, 14, 3]
// 对象参数默认值，如果参数为空，则会抛出异常
function show({title = “title”, width = 100, height = 200}) {
console.log(`${title} ${width} ${height}` );
}
show() // Cannot destructure property `title` of ‘undefined’ or ‘null’.
show({}) // title 100 200
// 解决办法：
function show({title = “title”, width = 100, height = 200} = {}) {
console.log(`${title} ${width} ${height}` );
}
show(); // title 100 200
show({width: 200}) // title 200 200
解析赋值
// key 变量重命名，first –> firstName
const person = {
first: ‘foo’,
last: ‘tom’,
};
const {first: firstName} = person;
console.log(firstName); // foo
// 默认值
const settings = {
speed: 150
}
const {speed = 750, width = 500} = settings;
console.log(speed); // 150
console.log(width); // 500
// 可能不存在的 key
const {middle: middleName = ‘midname’} = person;
console.log(middleName); // ‘midname’
// 嵌套赋值
const user = {
id: 339,
name: ‘Fred’,
age: 42,
education: {
degree: ‘Masters’
}
};
const {education: {degree}} = user;
console.log(degree); //prints: Masters
// 如果嵌套的属性不存在
const user = {
id: 339,
name: ‘Fred’,
age: 42
};
const {education: {degree}} = user; // TypeError: Cannot match against ‘undefined’ or ‘null’.
// 解决办法：
const user = {
id: 339,
name: ‘Fred’,
age: 42
};
const {education: {degree} = {}} = user;
console.log(degree); //prints: undefined
利用数组生成一个数字序列
const numRange = (start, end) => {
return Array(end – start + 1).fill().map((item, index) => start + index);
};
const numbers = numRange(0, 5); // [0, 1, 2, 3, 4, 5]
const numbers2 = numRange(1, 5); // [1, 2, 3, 4, 5]
利用 Set 给数组去重
const years = [2016, 2017, 2017, 2018, 2018, 2019]
// set 构造函数的参数是一个 array
const distinctYears = […new Set(years)] // [2016, 2017, 2018, 2019]
生成唯一随机字符串，可以指定长度
function generateRandom(length) {
let radom13chars = function () {
return Math.random().toString(16).substring(2, 15)
}
let loops = Math.ceil(length / 13)
return new Array(loops).fill(radom13chars).reduce((string, func) => {
return string + func()
}, ”).substring(0, length)
}
generateRandom(8) // “03836a49”
