JavaScript 作为网页样式的描述语言，在公司一直有着广泛的应用。本文档的目标是使 JavaScript 代码风格保持一致，容易理解和维护。
虽然本文档是针对 JavaScript 设计的，但是在使用其他编译到 JavaScript 的语言（TypeScript 等）时候，适用的部分也应尽量遵循本文档的约定。
UTF-8 不需要 BOM 来表明字节顺序，不要使用 Windows 的记事本改代码！
// bad
var a = 1;
var b = 2;
// good
const a = 1;
const b = 2;// bad
var count = 1;
if (true) {
count += 1;
}
// good, use the let.
let count = 1;
if (true) {
count += 1;
}// bad
const item = new Object();
// good
const item = {};function getKey(k) {
return `a key named ${k}`;
}
// bad
const obj = {
id: 5,
name: 'San Francisco',
};
obj[getKey('enabled')] = true;
// good
const obj = {
id: 5,
name: 'San Francisco',
[getKey('enabled')]: true,
};// bad
const atom = {
value: 1,
addValue: function (value) {
return atom.value + value;
},
};
// good
const atom = {
value: 1,
addValue(value) {
return atom.value + value;
},
};const lukeSkywalker = 'Luke Skywalker';
// bad
const obj = {
lukeSkywalker: lukeSkywalker,
};
// good
const obj = {
lukeSkywalker,
};const anakinSkywalker = 'Anakin Skywalker';
const lukeSkywalker = 'Luke Skywalker';
// bad
const obj = {
episodeOne: 1,
twoJediWalkIntoACantina: 2,
lukeSkywalker,
episodeThree: 3,
mayTheFourth: 4,
anakinSkywalker,
};
// good
const obj = {
lukeSkywalker,
anakinSkywalker,
episodeOne: 1,
twoJediWalkIntoACantina: 2,
episodeThree: 3,
mayTheFourth: 4,
};// bad
const bad = {
'foo': 3,
'bar': 4,
'data-blah': 5,
};
// good
const good = {
foo: 3,
bar: 4,
'data-blah': 5,
};// very bad
const original = { a: 1, b: 2 };
const copy = Object.assign(original, { c: 3 }); // this mutates `original` ಠ_ಠ
delete copy.a; // so does this
// bad
const original = { a: 1, b: 2 };
const copy = Object.assign({}, original, { c: 3 }); // copy => { a: 1, b: 2, c: 3 }
// good es6扩展运算符 ...
const original = { a: 1, b: 2 };
// 浅拷贝
const copy = { ...original, c: 3 }; // copy => { a: 1, b: 2, c: 3 }
// rest 赋值运算符
const { a, ...noA } = copy; // noA => { b: 2, c: 3 }// bad
const items = new Array();
// good
const items = [];const someStack = [];
// bad
someStack[someStack.length] = 'abracadabra';
// good
someStack.push('abracadabra');// bad
const len = items.length;
const itemsCopy = [];
let i;
for (i = 0; i < len; i += 1) {
itemsCopy[i] = items[i];
}
// good
const itemsCopy = [...items];const foo = document.querySelectorAll('.foo');
// good
const nodes = Array.from(foo);
// best
const nodes = [...foo];const arrLike = { 0: 'foo', 1: 'bar', 2: 'baz', length: 3 };
// bad
const arr = Array.prototype.slice.call(arrLike);
const arr = [].slice.call(arrLike);
// good
const arr = Array.from(arrLike);// good
[1, 2, 3].map((x) => {
const y = x + 1;
return x * y;
});
// good
[1, 2, 3].map(x => x + 1);
// bad - no returned value means `acc` becomes undefined after the first iteration
[[0, 1], [2, 3], [4, 5]].reduce((acc, item, index) => {
const flatten = acc.concat(item);
acc[index] = flatten;
});
// good
[[0, 1], [2, 3], [4, 5]].reduce((acc, item, index) => {
const flatten = acc.concat(item);
acc[index] = flatten;
return flatten;
});
// bad
inbox.filter((msg) => {
const { subject, author } = msg;
if (subject === 'Mockingbird') {
return author === 'Harper Lee';
} else {
return false;
}
});
// good
inbox.filter((msg) => {
const { subject, author } = msg;
if (subject === 'Mockingbird') {
return author === 'Harper Lee';
}
return false;
});// bad
const arr = [
[0, 1], [2, 3], [4, 5],
];
const objectInArray = [{
id: 1,
}, {
id: 2,
}];
const numberInArray = [
1, 2,
];
// good
const arr = [[0, 1], [2, 3], [4, 5]];
const objectInArray = [
{
id: 1,
},
{
id: 2,
},
];
const numberInArray = [
1,
2,
];const a = [
{ value: 2 },
{ value: 3 },
{ value: 4 },
];
// bad
const b = a.map(item => {
item.value = item.value * 2
});
// good
const b = a.map(item => {
return item.value * 2
});
const b = a.map(({ value }) => value * 2);// bad
function getFullName(user) {
const firstName = user.firstName;
const lastName = user.lastName;
return `${firstName} ${lastName}`;
}
// good
function getFullName(user) {
const { firstName, lastName } = user;
return `${firstName} ${lastName}`;
}
// best
function getFullName({ firstName, lastName }) {
return `${firstName} ${lastName}`;
}const arr = [1, 2, 3, 4];
// bad
const first = arr[0];
const second = arr[1];
// good
const [first, second] = arr;// bad
function processInput(input) {
// then a miracle occurs
return [left, right, top, bottom];
}
// the caller needs to think about the order of return data
const [left, __, top] = processInput(input);
// good
function processInput(input) {
// then a miracle occurs
return { left, right, top, bottom };
}
// the caller selects only the data they need
const { left, top } = processInput(input);// bad
const name = "Capt. Janeway";
// bad - template literals should contain interpolation or newlines
const name = `Capt. Janeway`;
// good
const name = 'Capt. Janeway';// bad
const errorMessage = 'This is a super long error that was thrown because \
of Batman. When you stop to think about how Batman had anything to do \
with this, you would get nowhere \
fast.';
// bad
const errorMessage = 'This is a super long error that was thrown because ' +
'of Batman. When you stop to think about how Batman had anything to do ' +
'with this, you would get nowhere fast.';
// good
const errorMessage = 'This is a super long error that was thrown because of Batman. When you stop to think about how Batman had anything to do with this, you would get nowhere fast.';// bad
function sayHi(name) {
return 'How are you, ' + name + '?';
}
// bad
function sayHi(name) {
return ['How are you, ', name, '?'].join();
}
// bad
function sayHi(name) {
return `How are you, ${ name }?`;
}
// good
function sayHi(name) {
return `How are you, ${name}?`;
}// bad
const foo = '\'this\' \i\s \"quoted\"';
// good
const foo = '\'this\' is "quoted"';
const foo = `my name is '${name}'`;// bad
const foo = function () {
// do something
}
// good
function foo () {
// do something
}// bad
(function () {
console.log('Welcome to the Internet. Please follow me.');
})();
// good
(function () {
console.log('Welcome to the Internet. Please follow me.');
}());// bad
if (isUse) {
function test () {
// do something
}
}
// good
let test
if (isUse) {
test = () => {
// do something
}
}// bad
function foo(name, options, arguments) {
// ...
}
// good
function foo(name, options, args) {
// ...
}
// bad
function concatenateAll() {
const args = Array.prototype.slice.call(arguments);
return args.join('');
}
// good
function concatenateAll(...args) {
return args.join('');
}// really bad
function handleThings(opts) {
// No! We shouldn’t mutate function arguments.
// Double bad: if opts is falsy it'll be set to an object which may
// be what you want but it can introduce subtle bugs.
opts = opts || {};
// ...
}
// still bad
function handleThings(opts) {
if (opts === void 0) {
opts = {};
}
// ...
}
// good
function handleThings(opts = {}) {
// ...
}var b = 1;
// bad
function count(a = b++) {
console.log(a);
}
count(); // 1
count(); // 2
count(3); // 3
count(); // 3// bad
function handleThings(opts = {}, name) {
// ...
}
// good
function handleThings(name, opts = {}) {
// ...
}真正需要用的时候除外。
// bad
var add = new Function('a', 'b', 'return a + b');
// still bad
var subtract = Function('a', 'b', 'return a - b');// bad
const f = function(){};
const g = function (){};
const h = function () {};
// good
const x = function() {};
const y = function a() {};// bad
function f1(obj) {
obj.key = 1;
}
// good
function f2(obj) {
const key = Object.prototype.hasOwnProperty.call(obj, 'key') ? obj.key : 1;
}// bad
function f1(a) {
a = 1;
// ...
}
function f2(a) {
if (!a) { a = 1; }
// ...
}
// good
function f3(a) {
const b = a || 1;
// ...
}
function f4(a = 1) {
// ...
}// bad
const x = [1, 2, 3, 4, 5];
console.log.apply(console, x);
// good
const x = [1, 2, 3, 4, 5];
console.log(...x);
// bad
new (Function.prototype.bind.apply(Date, [null, 2016, 8, 5]));
// good
new Date(...[2016, 8, 5]);// bad
function foo(bar,
baz,
quux) {
// ...
}
// good
function foo(
bar,
baz,
quux,
) {
// ...
}
// bad
console.log(foo,
bar,
baz);
// good
console.log(
foo,
bar,
baz,
);// bad
[1, 2, 3].map(function (x) {
const y = x + 1;
return x * y;
});
// good
[1, 2, 3].map(x => {
const y = x + 1;
return x * y;
});// bad
[1, 2, 3].map((x) => x * x);
// good
[1, 2, 3].map(x => x * x);
// good
[1, 2, 3].map(number => (
`A long string with the ${number}. It’s so long that we don’t want it to take up space on the .map line!`
));// bad
[1, 2, 3].map(number => {
const nextNumber = number + 1;
`A string containing the ${nextNumber}.`;
});
// good
[1, 2, 3].map(number => `A string containing the ${number}.`);
// good
[1, 2, 3].map(number => {
const nextNumber = number + 1;
return `A string containing the ${nextNumber}.`;
});// bad
function Queue(contents = []) {
this.queue = [...contents];
}
Queue.prototype.pop = function () {
const value = this.queue[0];
this.queue.splice(0, 1);
return value;
};
// good
class Queue {
constructor(contents = []) {
this.queue = [...contents];
}
pop() {
const value = this.queue[0];
this.queue.splice(0, 1);
return value;
}
}// bad
const inherits = require('inherits');
function PeekableQueue(contents) {
Queue.apply(this, contents);
}
inherits(PeekableQueue, Queue);
PeekableQueue.prototype.peek = function () {
return this.queue[0];
};
// good
class PeekableQueue extends Queue {
peek() {
return this.queue[0];
}
}// bad
class Jedi {
constructor() {}
getName() {
return this.name;
}
}
// bad
class Rey extends Jedi {
constructor(...args) {
super(...args);
}
}
// good
class Rey extends Jedi {
constructor(...args) {
super(...args);
this.name = 'Rey';
}
}// bad
class Foo {
bar() { return 1; }
bar() { return 2; }
}
// good
class Foo {
bar() { return 1; }
}
// good
class Foo {
bar() { return 2; }
}// bad
const AirbnbStyleGuide = require('./AirbnbStyleGuide');
module.exports = AirbnbStyleGuide.es6;
// ok
import AirbnbStyleGuide from './AirbnbStyleGuide';
export default AirbnbStyleGuide.es6;
// best
import { es6 } from './AirbnbStyleGuide';
export default es6;// bad
import * as AirbnbStyleGuide from './AirbnbStyleGuide';
// good
import AirbnbStyleGuide from './AirbnbStyleGuide';// bad
// filename es6.js
export { es6 as default } from './AirbnbStyleGuide';
// good
// filename es6.js
import { es6 } from './AirbnbStyleGuide';
export default es6;// bad
import foo from 'foo';
// … some other imports … //
import { named1, named2 } from 'foo';
// good
import foo, { named1, named2 } from 'foo';
// good
import foo, {
named1,
named2,
} from 'foo';// bad
import foo from 'foo';
foo.init();
import bar from 'bar';
// good
import foo from 'foo';
import bar from 'bar';
foo.init();// bad
import fooSass from 'css!sass!foo.scss';
import barCss from 'style!css!bar.css';
// good
import fooSass from 'foo.scss';
import barCss from 'bar.css';// bad
import {longNameA, longNameB, longNameC, longNameD, longNameE} from 'path';
// good
import {
longNameA,
longNameB,
longNameC,
longNameD,
longNameE,
} from 'path';// bad
export function foo() {}
// good
export default function foo() {}用数组的这些迭代方法： map() / every() / filter() / find() / findIndex() / reduce() / some() / ... , 用对象的这些方法 Object.keys() / Object.values() / Object.entries() 去产生一个数组， 这样你就能去遍历对象了。
const numbers = [1, 2, 3, 4, 5];
// bad
let sum = 0;
for (let num of numbers) {
sum += num;
}
sum === 15;
// good
let sum = 0;
numbers.forEach(num => sum += num);
sum === 15;
// best (use the functional force)
const sum = numbers.reduce((total, num) => total + num, 0);
sum === 15;
// bad
const increasedByOne = [];
for (let i = 0; i < numbers.length; i++) {
increasedByOne.push(numbers[i] + 1);
}
// good
const increasedByOne = [];
numbers.forEach(num => increasedByOne.push(num + 1));
// best (keeping it functional)
const increasedByOne = numbers.map(num => num + 1);// bad
function * foo() {
// ...
}
// bad
const bar = function * () {
// ...
}
// bad
const baz = function *() {
// ...
}
// bad
const quux = function* () {
// ...
}
// bad
function*foo() {
// ...
}
// bad
function *foo() {
// ...
}
// very bad
function
*
foo() {
// ...
}
// very bad
const wat = function
*
() {
// ...
}
// good
function* foo() {
// ...
}
// good
const foo = function*() {
// ...
}const luke = {
jedi: true,
age: 28,
};
// bad
const isJedi = luke['jedi'];
// good
const isJedi = luke.jedi;
function getProp(prop) {
return luke[prop];
}
const isJedi = getProp('jedi');// bad
const binary = Math.pow(2, 10);
// good
const binary = 2 ** 10;// bad
superPower = new SuperPower();
// bad
var superPower = new SuperPower();
// good
const superPower = new SuperPower();// bad
const items = getItems(),
goSportsTeam = true,
dragonball = 'z';
// bad
// (compare to above, and try to spot the mistake)
const items = getItems(),
goSportsTeam = true;
dragonball = 'z';
// good
const items = getItems();
const goSportsTeam = true;
const dragonball = 'z';let 和 const 都是块级作用域而不是函数级作用域
// bad - unnecessary function call
function checkName(hasName) {
const name = getName();
if (hasName === 'test') {
return false;
}
if (name === 'test') {
this.setName('');
return false;
}
return name;
}
// good
function checkName(hasName) {
if (hasName === 'test') {
return false;
}
// 在需要的时候分配
const name = getName();
if (name === 'test') {
this.setName('');
return false;
}
return name;
}// bad
(function example() {
// JavaScript interprets this as
// let a = ( b = ( c = 1 ) );
// The let keyword only applies to variable a; variables b and c become
// global variables.
let a = b = c = 1;
}());
console.log(a); // throws ReferenceError
console.log(b); // 1
console.log(c); // 1
// good
(function example() {
let a = 1;
let b = a;
let c = a;
}());
console.log(a); // throws ReferenceError
console.log(b); // throws ReferenceError
console.log(c); // throws ReferenceError
// the same applies for `const`// bad
const some_unused_var = 42;
// Write-only variables are not considered as used.
let y = 10;
y = 5;
// A read for a modification of itself is not considered as used.
let z = 0;
z = z + 1;
// Unused function arguments.
function getX(x, y) {
return x;
}
// good
function getXPlusY(x, y) {
return x + y;
}
const x = 1;
const y = a + 2;
alert(getXPlusY(x, y));
// 'type' is ignored even if unused because it has a rest property sibling.
// This is a form of extracting an object that omits the specified keys.
const { type, ...coords } = data;
// 'coords' is now the 'data' object without its 'type' property.// bad
let i, len, dragonball,
items = getItems(),
goSportsTeam = true;
// bad
let i;
const items = getItems();
let dragonball;
const goSportsTeam = true;
let len;
// good
const goSportsTeam = true;
const items = getItems();
let dragonball;
let i;
let length;// bad
if (isValid === true) {
// ...
}
// good
if (isValid) {
// ...
}
// bad
if (name) {
// ...
}
// good
if (name !== '') {
// ...
}
// bad
if (collection.length) {
// ...
}
// good
if (collection.length > 0) {
// ...
}// bad
switch (foo) {
case 1:
let x = 1;
break;
case 2:
const y = 2;
break;
case 3:
function f() {
// ...
}
break;
default:
class C {}
}
// good
switch (foo) {
case 1: {
let x = 1;
break;
}
case 2: {
const y = 2;
break;
}
case 3: {
function f() {
// ...
}
break;
}
case 4:
bar();
break;
default: {
class C {}
}
}// bad
const foo = maybe1 > maybe2
? "bar"
: value1 > value2 ? "baz" : null;
// better
const maybeNull = value1 > value2 ? 'baz' : null;
const foo = maybe1 > maybe2
? 'bar'
: maybeNull;
// best
const maybeNull = value1 > value2 ? 'baz' : null;
const foo = maybe1 > maybe2 ? 'bar' : maybeNull;// bad
const foo = a ? a : b;
const bar = c ? true : false;
const baz = c ? false : true;
// good
const foo = a || b;
const bar = !!c;
const baz = !c;// bad
const foo = a && b < 0 || c > 0 || d + 1 === 0;
// bad
const bar = a ** b - 5 % d;
// bad
// one may be confused into thinking (a || b) && c
if (a || b && c) {
return d;
}
// good
const foo = (a && b < 0) || c > 0 || (d + 1 === 0);
// good
const bar = (a ** b) - (5 % d);
// good
if (a || (b && c)) {
return d;
}
// good
const bar = a + b / c * d;// bad
if (test)
return false;
// good
if (test) return false;
// good
if (test) {
return false;
}
// bad
function foo() { return false; }
// good
function bar() {
return false;
}// bad
if (test) {
thing1();
thing2();
}
else {
thing3();
}
// good
if (test) {
thing1();
thing2();
} else {
thing3();
}3.13.3 [建议] 如果 if 语句中总是需要用 return 返回， 那后续的 else 就不需要写了。 if 块中包含 return， 它后面的 else if 块中也包含了 return， 这个时候就可以把 return 分到多个 if 语句块中
// bad
function foo() {
if (x) {
return x;
} else {
return y;
}
}
// bad
function cats() {
if (x) {
return x;
} else if (y) {
return y;
}
}
// bad
function dogs() {
if (x) {
return x;
} else {
if (y) {
return y;
}
}
}
// good
function foo() {
if (x) {
return x;
}
return y;
}
// good
function cats() {
if (x) {
return x;
}
if (y) {
return y;
}
}
// good
function dogs(x) {
if (x) {
if (z) {
return y;
}
} else {
return z;
}
}// bad
!isRunning && startRunning();
// good
if (!isRunning) {
startRunning();
}// bad
if ((foo === 123 || bar === 'abc') && doesItLookGoodWhenItBecomesThatLong() && isThisReallyHappening()) {
thing1();
}
// bad
if (foo === 123 &&
bar === 'abc') {
thing1();
}
// bad
if (foo === 123
&& bar === 'abc') {
thing1();
}
// bad
if (
foo === 123 &&
bar === 'abc'
) {
thing1();
}
// good
if (
foo === 123
&& bar === 'abc'
) {
thing1();
}
// good
if (
(foo === 123 || bar === 'abc')
&& doesItLookGoodWhenItBecomesThatLong()
&& isThisReallyHappening()
) {
thing1();
}
// good
if (foo === 123 && bar === 'abc') {
thing1();
}// bad
// make() returns a new element
// based on the passed in tag name
//
// @param {String} tag
// @return {Element} element
function make(tag) {
// ...
return element;
}
// good
/**
* make() returns a new element
* based on the passed-in tag name
*/
function make(tag) {
// ...
return element;
}// bad
const active = true; // is current tab
// good
// is current tab
const active = true;
// bad
function getType() {
console.log('fetching type...');
// set the default type to 'no type'
const type = this._type || 'no type';
return type;
}
// good
function getType() {
console.log('fetching type...');
// set the default type to 'no type'
const type = this._type || 'no type';
return type;
}
// also good
function getType() {
// set the default type to 'no type'
const type = this._type || 'no type';
return type;
}// bad
//is current tab
const active = true;
// good
// is current tab
const active = true;
// bad
/**
*make() returns a new element
*based on the passed-in tag name
*/
function make(tag) {
// ...
return element;
}
// good
/**
* make() returns a new element
* based on the passed-in tag name
*/
function make(tag) {
// ...
return element;
}class Calculator extends Abacus {
constructor() {
super();
// FIXME: shouldn't use a global here
total = 0;
}
}
class Calculator extends Abacus {
constructor() {
super();
// TODO: total should be configurable by an options param
this.total = 0;
}
}那是不是不能使用 tab 进行缩进了？大部分文本编辑器都有配置选项，也可以通过配置 .editorconfig ，将 tab 自动转换为空格。
// bad
function foo() {
∙∙∙∙const name;
}
// bad
function bar() {
∙const name;
}
// good
function baz() {
∙∙const name;
}// bad
function test(){
console.log('test');
}
// good
function test() {
console.log('test');
}
// bad
dog.set('attr',{
age: '1 year',
breed: 'Bernese Mountain Dog',
});
// good
dog.set('attr', {
age: '1 year',
breed: 'Bernese Mountain Dog',
});// bad
if(isJedi) {
fight ();
}
// good
if (isJedi) {
fight();
}
// bad
function fight () {
console.log ('Swooosh!');
}
// good
function fight() {
console.log('Swooosh!');
}// bad
const x=y+5;
// good
const x = y + 5;// bad
$('#items').find('.selected').highlight().end().find('.open').updateCount();
// bad
$('#items').
find('.selected').
highlight().
end().
find('.open').
updateCount();
// good
$('#items')
.find('.selected')
.highlight()
.end()
.find('.open')
.updateCount();
// bad
const leds = stage.selectAll('.led').data(data).enter().append('svg:svg').classed('led', true)
.attr('width', (radius + margin) * 2).append('svg:g')
.attr('transform', `translate(${radius + margin},${radius + margin})`)
.call(tron.led);
// good
const leds = stage.selectAll('.led')
.data(data)
.enter().append('svg:svg')
.classed('led', true)
.attr('width', (radius + margin) * 2)
.append('svg:g')
.attr('transform', `translate(${radius + margin},${radius + margin})`)
.call(tron.led);
// good
const leds = stage.selectAll('.led').data(data);// bad
if (foo) {
return bar;
}
return baz;
// good
if (foo) {
return bar;
}
return baz;
// bad
const obj = {
foo() {
},
bar() {
},
};
return obj;
// good
const obj = {
foo() {
},
bar() {
},
};
return obj;
// bad
const arr = [
function foo() {
},
function bar() {
},
];
return arr;
// good
const arr = [
function foo() {
},
function bar() {
},
];
return arr;// bad
function bar() {
console.log(foo);
}
// bad
if (baz) {
console.log(qux);
} else {
console.log(foo);
}
// bad
class Foo {
constructor(bar) {
this.bar = bar;
}
}
// good
function bar() {
console.log(foo);
}
// good
if (baz) {
console.log(qux);
} else {
console.log(foo);
}// bad
function bar( foo ) {
return foo;
}
// good
function bar(foo) {
return foo;
}
// bad
if ( foo ) {
console.log(foo);
}
// good
if (foo) {
console.log(foo);
}// bad
const foo = [ 1, 2, 3 ];
console.log(foo[ 0 ]);
// good
const foo = [1, 2, 3];
console.log(foo[0]);// bad
const foo = {clark: 'kent'};
// good
const foo = { clark: 'kent' };
// bad
function foo() {return true;}
if (foo) { bar = 0;}
// good
function foo() { return true; }
if (foo) { bar = 0; }// bad
var foo = 1,bar = 2;
var arr = [1 , 2];
// good
var foo = 1, bar = 2;
var arr = [1, 2];// bad
obj[foo ]
obj[ 'foo']
var x = {[ b ]: a}
obj[foo[ bar ]]
// good
obj[foo]
obj['foo']
var x = { [b]: a }
obj[foo[bar]]// bad
func ();
func
();
// good
func();// bad
var obj = { "foo" : 42 };
var obj2 = { "foo":42 };
// good
var obj = { "foo": 42 };// bad
var x = 1;
var y = 2;
// good
var x = 1;
var y = 2;特殊情况可以例外, 比如长 URL。
// bad
const foo = jsonData && jsonData.foo && jsonData.foo.bar && jsonData.foo.bar.baz && jsonData.foo.bar.baz.quux && jsonData.foo.bar.baz.quux.xyzzy;
// bad
$.ajax({ method: 'POST', url: 'https://airbnb.com/', data: { name: 'John' } }).done(() => console.log('Congratulations!')).fail(() => console.log('You have failed this city.'));
// good
const foo = jsonData
&& jsonData.foo
&& jsonData.foo.bar
&& jsonData.foo.bar.baz
&& jsonData.foo.bar.baz.quux
&& jsonData.foo.bar.baz.quux.xyzzy;
// good
$.ajax({
method: 'POST',
url: 'https://airbnb.com/',
data: { name: 'John' },
})
.done(() => console.log('Congratulations!'))
.fail(() => console.log('You have failed this city.'));// bad
const story = [
once
, upon
, aTime
];
// good
const story = [
once,
upon,
aTime,
];
// bad
const hero = {
firstName: 'Ada'
, lastName: 'Lovelace'
, birthYear: 1815
, superPower: 'computers'
};
// good
const hero = {
firstName: 'Ada',
lastName: 'Lovelace',
birthYear: 1815,
superPower: 'computers',
};// bad
const hero = {
firstName: 'Dana',
lastName: 'Scully'
};
const heroes = [
'Batman',
'Superman'
];
// good
const hero = {
firstName: 'Dana',
lastName: 'Scully',
};
const heroes = [
'Batman',
'Superman',
];
// bad
function createHero(
firstName,
lastName,
inventorOf
) {
// does nothing
}
// good
function createHero(
firstName,
lastName,
inventorOf,
) {
// does nothing
}
// good (note that a comma must not appear after a "rest" element)
function createHero(
firstName,
lastName,
inventorOf,
...heroArgs
) {
// does nothing
}
// bad
createHero(
firstName,
lastName,
inventorOf
);
// good
createHero(
firstName,
lastName,
inventorOf,
);
// good (note that a comma must not appear after a "rest" element)
createHero(
firstName,
lastName,
inventorOf,
...heroArgs
);本质上加与不加都没问题，但是为了统一，还是加。
// bad - raises exception
const luke = {}
const leia = {}
[luke, leia].forEach(jedi => jedi.father = 'vader')
// bad - raises exception
const reaction = "No! That’s impossible!"
(async function meanwhileOnTheFalcon() {
// handle `leia`, `lando`, `chewie`, `r2`, `c3p0`
// ...
}())
// bad - returns `undefined` instead of the value on the next line - always happens when `return` is on a line by itself because of ASI!
function foo() {
return
'search your feelings, you know it to be foo'
}
// good
const luke = {};
const leia = {};
[luke, leia].forEach((jedi) => {
jedi.father = 'vader';
});
// good
const reaction = "No! That’s impossible!";
(async function meanwhileOnTheFalcon() {
// handle `leia`, `lando`, `chewie`, `r2`, `c3p0`
// ...
}());
// good
function foo() {
return 'search your feelings, you know it to be foo';
}// => this.reviewScore = 9;
// bad
const totalScore = new String(this.reviewScore); // typeof totalScore is "object" not "string"
// bad
const totalScore = this.reviewScore + ''; // invokes this.reviewScore.valueOf()
// bad
const totalScore = this.reviewScore.toString(); // isn’t guaranteed to return a string
// good
const totalScore = String(this.reviewScore);const inputValue = '4';
// bad
const val = new Number(inputValue);
// bad
const val = +inputValue;
// bad
const val = inputValue >> 0;
// bad
const val = parseInt(inputValue);
// good
const val = Number(inputValue);
// good
const val = parseInt(inputValue, 10);const age = 0;
// bad
const hasAge = new Boolean(age);
// good
const hasAge = Boolean(age);
// best
const hasAge = !!age;// bad
function q() {
// ...
}
// good
function query() {
// ...
}// bad
const OBJEcttsssss = {};
const this_is_my_object = {};
function c() {}
// good
const thisIsMyObject = {};
function thisIsMyFunction() {}// bad
function user(options) {
this.name = options.name;
}
const bad = new user({
name: 'nope',
});
// good
class User {
constructor(options) {
this.name = options.name;
}
}
const good = new User({
name: 'yup',
});// bad
this.__firstName__ = 'Panda';
this.firstName_ = 'Panda';
this._firstName = 'Panda';
// good
this.firstName = 'Panda';
// good, in environments where WeakMaps are available
// see https://kangax.github.io/compat-table/es6/#test-WeakMap
const firstNames = new WeakMap();
firstNames.set(this, 'Panda');// bad
function foo() {
const self = this;
return function () {
console.log(self);
};
}
// bad
function foo() {
const that = this;
return function () {
console.log(that);
};
}
// good
function foo() {
return () => {
console.log(this);
};
}// file 1 contents
class CheckBox {
// ...
}
export default CheckBox;
// file 2 contents
export default function fortyTwo() { return 42; }
// file 3 contents
export default function insideDirectory() {}
// in some other file
// bad
import CheckBox from './checkBox'; // PascalCase import/export, camelCase filename
import FortyTwo from './FortyTwo'; // PascalCase import/filename, camelCase export
import InsideDirectory from './InsideDirectory'; // PascalCase import/filename, camelCase export
// bad
import CheckBox from './check_box'; // PascalCase import/export, snake_case filename
import forty_two from './forty_two'; // snake_case import/filename, camelCase export
import inside_directory from './inside_directory'; // snake_case import, camelCase export
import index from './inside_directory/index'; // requiring the index file explicitly
import insideDirectory from './insideDirectory/index'; // requiring the index file explicitly
// good
import CheckBox from './CheckBox'; // PascalCase export/import/filename
import fortyTwo from './fortyTwo'; // camelCase export/import/filename
import insideDirectory from './insideDirectory'; // camelCase export/import/directory name/implicit "index"
// supports both insideDirectory.js and insideDirectory/index.jsfunction makeStyleGuide() {
// ...
}
export default makeStyleGuide;const AirbnbStyleGuide = {
es6: {
}
};
export default AirbnbStyleGuide;// bad
import SmsContainer from './containers/SmsContainer';
// bad
const HttpRequests = [
// ...
];
// good
import SMSContainer from './containers/SMSContainer';
// good
const HTTPRequests = [
// ...
];
// also good
const httpRequests = [
// ...
];
// best
import TextMessageContainer from './containers/TextMessageContainer';
// best
const requests = [
// ...
];- 被导出的
- 是 const 定义的，保证不能被改变
- 这个变量是可信的，他的子属性都是不能被改变的
// bad
const PRIVATE_VARIABLE = 'should not be unnecessarily uppercased within a file';
// bad
export const THING_TO_BE_CHANGED = 'should obviously not be uppercased';
// bad
export let REASSIGNABLE_VARIABLE = 'do not use let with uppercase variables';
// ---
// allowed but does not supply semantic value
export const apiKey = 'SOMEKEY';
// better in most cases
export const API_KEY = 'SOMEKEY';
// ---
// bad - unnecessarily uppercases key while adding no semantic value
export const MAPPING = {
KEY: 'value'
};
// good
export const MAPPING = {
key: 'value'
};可能会产生副作用，难以理解。
// bad
class Dragon {
get age() {
// ...
}
set age(value) {
// ...
}
}
// good
class Dragon {
getAge() {
// ...
}
setAge(value) {
// ...
}
}// bad
if (!dragon.age()) {
return false;
}
// good
if (!dragon.hasAge()) {
return false;
}class Jedi {
constructor(options = {}) {
const lightsaber = options.lightsaber || 'blue';
this.set('lightsaber', lightsaber);
}
set(key, val) {
this[key] = val;
}
get(key) {
return this[key];
}
}// bad
$(this).trigger('listingUpdated', listing.id);
// ...
$(this).on('listingUpdated', (e, listingID) => {
// do something with listingID
});
// prefer:
// good
$(this).trigger('listingUpdated', { listingID: listing.id });
// ...
$(this).on('listingUpdated', (e, data) => {
// do something with data.listingID
});// bad
const sidebar = $('.sidebar');
// good
const $sidebar = $('.sidebar');
// good
const $sidebarBtn = $('.sidebar-btn');// bad
function setSidebar() {
$('.sidebar').hide();
// ...
$('.sidebar').css({
'background-color': 'pink',
});
}
// good
function setSidebar() {
const $sidebar = $('.sidebar');
$sidebar.hide();
// ...
$sidebar.css({
'background-color': 'pink',
});
}// bad
$('ul', '.sidebar').hide();
// bad
$('.sidebar').find('ul').hide();
// good
$('.sidebar ul').hide();
// good
$('.sidebar > ul').hide();
// good
$sidebar.find('ul').hide();// bad
isNaN('1.2'); // false
isNaN('1.2.3'); // true
// good
Number.isNaN('1.2.3'); // false
Number.isNaN(Number('1.2.3')); // true// bad
isFinite('2e3'); // true
// good
Number.isFinite('2e3'); // false
Number.isFinite(parseInt('2e3', 10)); // true