Airbnb JavaScript 风格指南

2019-01-15  本文已影响0人  南方帅

规范原则： 不可变原则 统一化原则 易读易维护

类型

const foo = [1, 2];
const bar = foo;
bar[0] = 9;
console.log(foo[0], bar[0]); // => 9, 9

赋值

{
  let a = 1;
  const b = 1;
}
console.log(a); // ReferenceError
console.log(b); // ReferenceError

对象

// bad
var item = new Object();

// good
var 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,

  // 对象的方法
  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,
};

// bad
console.log(object.hasOwnProperty(key));

// good
console.log(Object.prototype.hasOwnProperty.call(object, key));

// best
const has = Object.prototype.hasOwnProperty; // cache the lookup once, in module scope.
/* or */
import has from 'has'; // https://www.npmjs.com/package/has
// ...
console.log(has.call(object, key));

// 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
const original = { a: 1, b: 2 };
const copy = { ...original, c: 3 }; // copy => { a: 1, b: 2, c: 3 }

const { a, ...noA } = copy; // noA => { b: 2, c: 3 }

数组

// bad
var items = new Array();

// good
var 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);

// good
const arr = Array.from(arrLike);

// bad
const baz = [...foo].map(bar);
// good
const baz = Array.from(foo, baz);

// good
[1, 2, 3].map((x) => {
  const y = x + 1;
  return x * y;
});

// good 函数只有一个语句
[1, 2, 3].map(x => x + 1);

// bad - 没有返回值， 因为在第一次迭代后acc 就变成undefined了
[[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,
];

解构

// 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);

字符串

// 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}'`;

函数

函数表达式： const func = function () {}
函数声明： function func() {}
函数申明作用域被提前，而且很容易在其定义之前被引用。这样会破坏代码可读性和维护性

// bad
function foo() {
  // ...
}

// bad
const foo = function () {
  // ...
};

// good
// lexical name distinguished from the variable-referenced invocation(s)
const short = function longUniqueMoreDescriptiveLexicalFoo() {
  // ...
};

// immediately-invoked function expression (IIFE)
(function () {
  console.log('Welcome to the Internet. Please follow me.');
}());

// bad
if (currentUser) {
  function test() {
    console.log('Nope.');
  }
}

// good
let test;
if (currentUser) {
  test = () => {
    console.log('Yup.');
  };
}

// 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) {
  // 不， 我们不该改arguments
  // 第二： 如果 opts 的值为 false, 它会被赋值为 {}
  // 虽然你想这么写， 但是这个会带来一些细微的bug
  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
// 所以 a到底是什么

// bad
function handleThings(opts = {}, name) {
  // ...
}

// good
function handleThings(name, opts = {}) {
  // ...
}

// 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,
);

箭头函数

Why? 他创建了一个this的当前执行上下文的函数的版本，这通常就是你想要的；而且箭头函数是更简洁的语法
Why? 什么时候不用箭头函数： 如果你有一个相当复杂的函数，你可能会把这个逻辑移出到他自己的函数声明里。

// 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(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}.`;
});

// good
[1, 2, 3].map((number, index) => ({
  [index]: number
}));

// 表达式有副作用就不要用隐式return
function foo(callback) {
  const val = callback();
  if (val === true) {
    // Do something if callback returns true
  }
}

let bool = false;

// bad
// 这种情况会return bool = true, 不好
foo(() => bool = true);

// good
foo(() => {
  bool = true;
});

// bad
['get', 'post', 'put'].map(httpMethod => Object.prototype.hasOwnProperty.call(
    httpMagicObjectWithAVeryLongName,
    httpMethod
  )
);

// good
['get', 'post', 'put'].map(httpMethod => (
  Object.prototype.hasOwnProperty.call(
    httpMagicObjectWithAVeryLongName,
    httpMethod
  )
));

// 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(x => {
  const y = x + 1;
  return x * y;
});

// good
[1, 2, 3].map((x) => {
  const y = x + 1;
  return x * y;
});

// bad
const itemHeight = item => item.height > 256 ? item.largeSize : item.smallSize;

// bad
const itemHeight = (item) => item.height > 256 ? item.largeSize : item.smallSize;

// good
const itemHeight = item => (item.height > 256 ? item.largeSize : item.smallSize);

// good
const itemHeight = (item) => {
  const { height, largeSize, smallSize } = item;
  return height > 256 ? largeSize : smallSize;
};

// bad
foo =>
  bar;

foo =>
  (bar);

// good
foo => bar;
foo => (bar);
foo => (
   bar
)

类名和构造函数

// 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
Jedi.prototype.jump = function () {
  this.jumping = true;
  return true;
};

Jedi.prototype.setHeight = function (height) {
  this.height = height;
};

const luke = new Jedi();
luke.jump(); // => true
luke.setHeight(20); // => undefined

// good
class Jedi {
  jump() {
    this.jumping = true;
    return this;
  }

  setHeight(height) {
    this.height = height;
    return this;
  }
}

const luke = new Jedi();

luke.jump()
  .setHeight(20);

// 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; }
}

模块

// 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
let foo = 3;
export { foo }

// good
const foo = 3;
export { foo }

// bad
export function foo() {}

// good
export default function foo() {}

// bad
import foo from 'foo';
foo.init();

import bar from 'bar';

// good
import foo from 'foo';
import bar from 'bar';

foo.init();

// good
import {
longNameA,
longNameB,
longNameC,
longNameD,
longNameE,
} from 'path';

// 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';

迭代器和生成器

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);


// good
function* foo() {
  // ...
}

// good
const foo = function* () {
  // ...
};

属性

const luke = {
  jedi: true,
  age: 28,
};

// bad
const isJedi = luke['jedi'];

// good
const isJedi = luke.jedi;

const luke = {
  jedi: true,
  age: 28,
};

function getProp(prop) {
  return luke[prop];
}

const isJedi = getProp('jedi');

// bad
const binary = Math.pow(2, 10);

// good
const binary = 2 ** 10;

变量

// bad
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';

// 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 - 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;
  }

  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 array = [1, 2, 3];
let num = 1;
num++;
--num;

let sum = 0;
let truthyCount = 0;
for (let i = 0; i < array.length; i++) {
  let value = array[i];
  sum += value;
  if (value) {
    truthyCount++;
  }
}

// good

const array = [1, 2, 3];
let num = 1;
num += 1;
num -= 1;

const sum = array.reduce((a, b) => a + b, 0);
const truthyCount = array.filter(Boolean).length;

// bad
const foo =
  superLongLongLongLongLongLongLongLongFunctionName();

// bad
const foo
  = 'superLongLongLongLongLongLongLongLongString';

// good
const foo = (
  superLongLongLongLongLongLongLongLongFunctionName()
);

// good
const foo = 'superLongLongLongLongLongLongLongLongString';

// bad

var some_unused_var = 42;

// Write-only variables are not considered as used.
var y = 10;
y = 5;

// A read for a modification of itself is not considered as used.
var z = 0;
z = z + 1;

// Unused function arguments.
function getX(x, y) {
    return x;
}

// good

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

var x = 1;
var 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.
var { type, ...coords } = data;
// 'coords' is now the 'data' object without its 'type' property.

提升作用域

function example() {
  console.log(anonymous); // => undefined

  anonymous(); // => TypeError anonymous is not a function

  var anonymous = function () {
    console.log('anonymous function expression');
  };
}

比较运算符

if ([0] && []) {
  // true
  // 数组（即使是空数组）是对象，对象会计算成true
}

// 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
// 别人会陷入(a || b) && c 的迷惑中
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;

块

// 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();
}

// 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
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
!isRunning && startRunning();

// good
if (!isRunning) {
  startRunning();
}

注释

// 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;
  }
}

空格

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;

// good
import { es6 } from './AirbnbStyleGuide';
  // ...
export default es6;↵

// 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， 逗号分隔符还是要空格的
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;

逗号

// 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 - 没有结尾逗号的 git diff
const hero = {
     firstName: 'Florence',
-    lastName: 'Nightingale'
+    lastName: 'Nightingale',
+    inventorOf: ['coxcomb chart', 'modern nursing']
};

// good - 有结尾逗号的 git diff
const hero = {
     firstName: 'Florence',
     lastName: 'Nightingale',
+    inventorOf: ['coxcomb chart', 'modern nursing'],
};

分号

Why? 当 JavaScript 遇到没有分号结尾的一行，它会执行自动插入分号 Automatic Semicolon Insertion这一规则来决定行末是否加分号。如果JavaScript在你的断行里错误的插入了分号，就会出现一些古怪的行为。当新的功能加到JavaScript里后， 这些规则会变得更复杂难懂。显示的结束语句，并通过配置代码检查去捕获没有带分号的地方可以帮助你防止这种错误。

// bad
(function () {
  const name = 'Skywalker'
  return name
})()

// good
(function () {
  const name = 'Skywalker';
  return name;
}());

// good, 行首加分号，避免文件被连接到一起时立即执行函数被当做变量来执行。
;(() => {
  const name = 'Skywalker';
  return name;
}());

类型强制转化

// 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(); // 不保证返回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;

命名

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',
});

Why? JavaScript 没有私有属性或私有方法的概念。尽管前置下划线通常的概念上意味着“private”，事实上，这些属性是完全公有的，因此这部分也是你的API的内容。这一概念可能会导致开发者误以为更改这个不会导致崩溃或者不需要测试。 如果你想要什么东西变成“private”，那就不要让它在这里出现。

// bad
this.__firstName__ = 'Panda';
this.firstName_ = 'Panda';
this._firstName = 'Panda';

// good
this.firstName = '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.js

function 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 = [
  // ...
];

// best
import TextMessageContainer from './containers/TextMessageContainer';

// best
const Requests = [
  // ...
];

导出变量
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
Why? 这是一个附加工具，帮助开发者去辨识一个变量是不是不可变的。

对于所有的 const 变量呢？ —— 这个是不必要的。大写变量不应该在同一个文件里定义并使用， 它只能用来作为导出变量。 赞同！
那导出的对象呢？ —— 大写变量处在export的最高级(e.g. EXPORTED_OBJECT.key) 并且他包含的所有子属性都是不可变的。

// 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'
};

访问器

// 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];
  }
}

事件

jQuery

// 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();

ES5 兼容性

ECMAScript 6+ (ES 2015+) Styles

  1. 箭头函数——Arrow Functions
  2. 类——Classes
  3. 对象缩写——Object Shorthand
  4. 对象简写——Object Concise
  5. 对象计算属性——Object Computed Properties
  6. 模板字符串——Template Strings
  7. 解构赋值——Destructuring
  8. 默认参数——Default Parameters
  9. Rest
  10. Array Spreads
  11. Let and Const
  12. 幂操作符——Exponentiation Operator
  13. 迭代器和生成器——Iterators and Generators
  14. 模块——Modules

标准库

// 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
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