(1)传参使用默认值
// Bad:
function createMicrobrewery( name ) {
const breweryName = name || 'Hipster Brew Co.';
// ...
}
// Good:
function createMicrobrewery( name = 'Hipster Brew Co.' ) {
// ...
}
(2)函数参数( 最好 2 个或更少 )
如果参数超过两个，建议使用 ES6 的解构语法，不用考虑参数的顺序。
// Bad:
function createMenu( title, body, buttonText, cancellable ) {
// ...
}
// Good:
function createMenu( { title, body, buttonText, cancellable } ) {
// ...
}
createMenu({
title: 'Foo',
body: 'Bar',
buttonText: 'Baz',
cancellable: true
});
(3)一个方法只做一件事情
这是一条在软件工程领域流传久远的规则。严格遵守这条规则会让你的代码可读性更好，也更容易重构。
// Bad:
function emailClients( clients ) {
clients.forEach( client => {
const clientRecord = database.lookup( client );
if ( clientRecord.isActive() ) {
email( client );
}
});
}
// Good:
function emailActiveClients( clients ) {
clients
.filter( isActiveClient )
.forEach( email );
}
function isActiveClient( client ) {
const clientRecord = database.lookup( client );
return clientRecord.isActive();
}
(4)删除重复代码，合并相似函数
很多时候虽然是同一个功能，但由于一两个不同点，让你不得不写两个几乎相同的函数。
// Bad:
function showDeveloperList(developers) {
developers.forEach((developer) => {
const expectedSalary = developer.calculateExpectedSalary();
const experience = developer.getExperience();
const githubLink = developer.getGithubLink();
const data = {
expectedSalary,
experience,
githubLink
};
render(data);
});
}
function showManagerList(managers) {
managers.forEach((manager) => {
const expectedSalary = manager.calculateExpectedSalary();
const experience = manager.getExperience();
const portfolio = manager.getMBAProjects();
const data = {
expectedSalary,
experience,
portfolio
};
render(data);
});
}
// Good:
function showEmployeeList(employees) {
employees.forEach(employee => {
const expectedSalary = employee.calculateExpectedSalary();
const experience = employee.getExperience();
const data = {
expectedSalary,
experience,
};
switch(employee.type) {
case 'develop':
data.githubLink = employee.getGithubLink();
break
case 'manager':
data.portfolio = employee.getMBAProjects();
break
}
render(data);
})
}
(5)使用 Object.assign 设置默认属性
// Bad:
const menuConfig = {
title: null,
body: 'Bar',
buttonText: null,
cancellable: true
};
function createMenu(config) {
config.title = config.title || 'Foo';
config.body = config.body || 'Bar';
config.buttonText = config.buttonText || 'Baz';
config.cancellable = config.cancellable !== undefined ? config.cancellable : true;
}
createMenu(menuConfig);
// Good:
const menuConfig = {
title: 'Order',
// 不包含 body
buttonText: 'Send',
cancellable: true
};
function createMenu(config) {
config = Object.assign({
title: 'Foo',
body: 'Bar',
buttonText: 'Baz',
cancellable: true
}, config);
// config : {title: "Order", body: "Bar", buttonText: "Send", cancellable: true}
// ...
}
createMenu(menuConfig);
(6) 尽量不要写全局方法
在 JavaScript 中，永远不要污染全局，会在生产环境中产生难以预料的 bug。
举个例子，比如你在 Array.prototype 上新增一个 diff 方法来判断两个数组的不同。而你同事也打算做类似的事情，不过他的 diff 方法是用来判断两个数组首位元素的不同。很明显你们方法会产生冲突，遇到这类问题我们可以用 ES2015/ES6 的语法来对 Array 进行扩展。
// Bad:
Array.prototype.diff = function diff(comparisonArray) {
const hash = new Set(comparisonArray);
return this.filter(elem => !hash.has(elem));
};
// Good:
class SuperArray extends Array {
diff(comparisonArray) {
const hash = new Set(comparisonArray);
return this.filter(elem => !hash.has(elem));
}
}
(7) 尽量别用“非”条件句
// Bad:
function isDOMNodeNotPresent(node) {
// ...
}
if (!isDOMNodeNotPresent(node)) {
// ...
}
// Good:
function isDOMNodePresent(node) {
// ...
}
if (isDOMNodePresent(node)) {
// ...
}
(8) 尽量不要写全局方法
在 ES6 之前，没有类的语法，只能用构造函数的方式模拟类，可读性非常差。
// Good:
// 动物
class Animal {
constructor(age) {
this.age = age
};
move() {};
}
// 哺乳动物
class Mammal extends Animal{
constructor(age, furColor) {
super(age);
this.furColor = furColor;
};
liveBirth() {};
}
// 人类
class Human extends Mammal{
constructor(age, furColor, languageSpoken) {
super(age, furColor);
this.languageSpoken = languageSpoken;
};
speak() {};
}
(9) 使用链式调用
这种模式相当有用，可以在很多库中都有使用。它让你的代码简洁优雅。
// Bad:
class Car {
constructor(make, model, color) {
this.make = make;
this.model = model;
this.color = color;
}
setMake(make) {
this.make = make;
}
setModel(model) {
this.model = model;
}
setColor(color) {
this.color = color;
}
save() {
console.log(this.make, this.model, this.color);
}
}
const car = new Car('Ford','F-150','red');
car.setColor('pink');
car.save();
// Good:
class Car {
constructor(make, model, color) {
this.make = make;
this.model = model;
this.color = color;
}
setMake(make) {
this.make = make;
// NOTE: Returning this for chaining
return this;
}
setModel(model) {
this.model = model;
// NOTE: Returning this for chaining
return this;
}
setColor(color) {
this.color = color;
// NOTE: Returning this for chaining
return this;
}
save() {
console.log(this.make, this.model, this.color);
// NOTE: Returning this for chaining
return this;
}
}
const car = new Car("Ford", "F-150", "red").setColor("pink").save();
(10) 使用 promise 或者 Async/Await 代替回调
// Bad:
get('https://en.wikipedia.org/wiki/Robert_Cecil_Martin', (requestErr, response) => {
if (requestErr) {
console.error(requestErr);
} else {
writeFile('article.html', response.body, (writeErr) => {
if (writeErr) {
console.error(writeErr);
} else {
console.log('File written');
}
});
}
});
// Good:
get('https://en.wikipedia.org/wiki/Robert_Cecil_Martin')
.then((response) => {
return writeFile('article.html', response);
})
.then(() => {
console.log('File written');
})
.catch((err) => {
console.error(err);
});
// perfect:
async function getCleanCodeArticle() {
try {
const response = await get('https://en.wikipedia.org/wiki/Robert_Cecil_Martin');
await writeFile('article.html', response);
console.log('File written');
} catch(err) {
console.error(err);
}
}