摘要：如何提高代碼的可讀性復(fù)用性擴(kuò)展性。嚴(yán)格遵守這條規(guī)則會(huì)讓你的代碼可讀性更好，也更容易重構(gòu)。如果違反這個(gè)規(guī)則，那么代碼會(huì)很難被測(cè)試或者重用。它讓你的代碼簡(jiǎn)潔優(yōu)雅。

原文：https://github.com/ryanmcderm...  
說(shuō)明：本文翻譯自 github 上的一個(gè)項(xiàng)目，非全文搬運(yùn)，只取部分精華。

如何提高代碼的可讀性、復(fù)用性、擴(kuò)展性。我們將從以下四個(gè)方面討論：

變量

函數(shù)

類

異步

// Bad:
const yyyymmdstr = moment().format("YYYY/MM/DD");
// Good:
const currentDate = moment().format("YYYY/MM/DD");

對(duì)同一類型的變量使用相同的命名保持統(tǒng)一：

// Bad:
getUserInfo();
getClientData();
getCustomerRecord();
// Good:
getUser()

可以用 ESLint 檢測(cè)代碼中未命名的常量。

// Bad:
// 其他人知道 86400000 的意思嗎？
setTimeout( blastOff, 86400000 );
// Good:
const MILLISECOND_IN_A_DAY = 86400000;
setTimeout( blastOff, MILLISECOND_IN_A_DAY );

既然創(chuàng)建了一個(gè) car 對(duì)象，就沒(méi)有必要把它的顏色命名為 carColor。

// Bad:
const car = {
    carMake: "Honda",
    carModel: "Accord",
    carColor: "Blue"
};
function paintCar( car ) {
    car.carColor = "Red";
}
// Good:
const car = {
    make: "Honda",
    model: "Accord",
    color: "Blue"
};
function paintCar( car ) {
    car.color = "Red";
}

// Bad:
function createMicrobrewery( name ) {
    const breweryName = name || "Hipster Brew Co.";
    // ...
}
// Good:
function createMicrobrewery( name = "Hipster Brew Co." ) {
    // ...
}

如果參數(shù)超過(guò)兩個(gè)，建議使用 ES6 的解構(gòu)語(yǔ)法，不用考慮參數(shù)的順序。

// Bad:
function createMenu( title, body, buttonText, cancellable ) {
    // ...
}
// Good:
function createMenu( { title, body, buttonText, cancellable } ) {
    // ...
}
createMenu({
    title: "Foo",
    body: "Bar",
    buttonText: "Baz",
    cancellable: true
});

這是一條在軟件工程領(lǐng)域流傳久遠(yuǎn)的規(guī)則。嚴(yán)格遵守這條規(guī)則會(huì)讓你的代碼可讀性更好，也更容易重構(gòu)。如果違反這個(gè)規(guī)則，那么代碼會(huì)很難被測(cè)試或者重用。

// 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();
}

// Bad:
function addToDate( date, month ) {
    // ...
}
const date = new Date();
// 很難知道是把什么加到日期中
addToDate( date, 1 );
// Good:
function addMonthToDate( month, date ) {
    // ...
}
const date = new Date();
addMonthToDate( 1, date );

很多時(shí)候雖然是同一個(gè)功能，但由于一兩個(gè)不同點(diǎn)，讓你不得不寫(xiě)兩個(gè)幾乎相同的函數(shù)。

// 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);
  })
}

// 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);

在 JavaScript 中，永遠(yuǎn)不要污染全局，會(huì)在生產(chǎn)環(huán)境中產(chǎn)生難以預(yù)料的 bug。舉個(gè)例子，比如你在 Array.prototype 上新增一個(gè) diff 方法來(lái)判斷兩個(gè)數(shù)組的不同。而你同事也打算做類似的事情，不過(guò)他的 diff 方法是用來(lái)判斷兩個(gè)數(shù)組首位元素的不同。很明顯你們方法會(huì)產(chǎn)生沖突，遇到這類問(wèn)題我們可以用 ES2015/ES6 的語(yǔ)法來(lái)對(duì) Array 進(jìn)行擴(kuò)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));        
  }
}

// Bad:
function isDOMNodeNotPresent(node) {
  // ...
}
if (!isDOMNodeNotPresent(node)) {
  // ...
}
// Good:
function isDOMNodePresent(node) {
  // ...
}
if (isDOMNodePresent(node)) {
  // ...
}

現(xiàn)代瀏覽器已經(jīng)在底層做了很多優(yōu)化，過(guò)去的很多優(yōu)化方案都是無(wú)效的，會(huì)浪費(fèi)你的時(shí)間。

// Bad:
// 現(xiàn)代瀏覽器已對(duì)此( 緩存 list.length )做了優(yōu)化。
for (let i = 0, len = list.length; i < len; i++) {
  // ...
}
// Good:
for (let i = 0; i < list.length; i++) {
  // ...
}

這里沒(méi)有實(shí)例代碼，刪除就對(duì)了

在 ES6 之前，沒(méi)有類的語(yǔ)法，只能用構(gòu)造函數(shù)的方式模擬類，可讀性非常差。

// Good:
// 動(dòng)物
class Animal {
  constructor(age) {
    this.age = age
  };
  move() {};
}
// 哺乳動(dòng)物
class Mammal extends Animal{
  constructor(age, furColor) {
    super(age);
    this.furColor = furColor;
  };
  liveBirth() {};
}
// 人類
class Human extends Mammal{
  constructor(age, furColor, languageSpoken) {
    super(age, furColor);
    this.languageSpoken = languageSpoken;
  };
  speak() {};
}

這種模式相當(dāng)有用，可以在很多庫(kù)中都有使用。它讓你的代碼簡(jiǎn)潔優(yōu)雅。

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);
  }
}
// Bad:
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();

// 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);
  }
}

如果你想進(jìn)【大前端交流群】，關(guān)注公眾號(hào)點(diǎn)擊“交流加群”添加機(jī)器人自動(dòng)拉你入群。關(guān)注我第一時(shí)間接收最新干貨。