整潔的javascript代碼

變量

1.使用直觀且有意義的變量名

Bad:

const yyyymmdstr = moment().format("YYYY/MM/DD");

Good:

const currentDate = moment().format("YYYY/MM/DD");

2.對相同類型的變量使用相同的詞彙

Bad:

getUserInfo();
getClientData();
getCustomerRecord();

Good:

getUser();

3.使用可讀可推敲的變量

Bad:

setTimeout(blastOff, 86400000);

Good:

const MILLISECONDS_IN_A_DAY = 86400000;

setTimeout(blastOff, MILLISECONDS_IN_A_DAY);

4.使用具有解釋性的變量

Bad:

const address = "One Infinite Loop, Cupertino 95014";
const cityZipCodeRegex = /^[^,\\]+[,\\\s]+(.+?)\s*(\d{5})?$/;
saveCityZipCode(
  address.match(cityZipCodeRegex)[1],
  address.match(cityZipCodeRegex)[2]
);

Good:

const address = "One Infinite Loop, Cupertino 95014";
const cityZipCodeRegex = /^[^,\\]+[,\\\s]+(.+?)\s*(\d{5})?$/;
const [_, city, zipCode] = address.match(cityZipCodeRegex) || [];
saveCityZipCode(city, zipCode);

5.避免使用無意義的隱式變量名

Bad:

const locations = ["Austin", "New York", "San Francisco"];
locations.forEach(l => {
  doStuff();
  doSomeOtherStuff();
  // ...
  // ...
  // ...
  // Wait, what is `l` for again?
  dispatch(l);
});

Good:

const locations = ["Austin", "New York", "San Francisco"];
locations.forEach(location => {
  doStuff();
  doSomeOtherStuff();
  // ...
  // ...
  // ...
  dispatch(location);
});

6.不要給變量名加上不必要的作用域

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";
}

7.使用默認參數代替條件判斷

Bad:

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

Good:

function createMicrobrewery(name = "Hipster Brew Co.") {
  // ...
}

函數

1.函數參數個數不建議超過3個

Bad:

function createMenu(title, body, buttonText, cancellable) {
  // ...
}

createMenu("Foo", "Bar", "Baz", true);

Good:

function createMenu({ title, body, buttonText, cancellable }) {
  // ...
}

createMenu({
  title: "Foo",
  body: "Bar",
  buttonText: "Baz",
  cancellable: true
});

2.函數作用應該單一

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();
}

3.函數名應具有可讀性

Bad:

function addToDate(date, month) {
  // ...
}

const date = new Date();

// It's hard to tell from the function name what is added
addToDate(date, 1);

Good:

function emailActiveClients(clients) {
  clients.filter(isActiveClient).forEach(email);
}

function isActiveClient(client) {
  const clientRecord = database.lookup(client);
  return clientRecord.isActive();
}

4.函數不能過於抽象

Bad:

function parseBetterJSAlternative(code) {
  const REGEXES = [
    // ...
  ];

  const statements = code.split(" ");
  const tokens = [];
  REGEXES.forEach(REGEX => {
    statements.forEach(statement => {
      // ...
    });
  });

  const ast = [];
  tokens.forEach(token => {
    // lex...
  });

  ast.forEach(node => {
    // parse...
  });
}

Good:

function parseBetterJSAlternative(code) {
  const tokens = tokenize(code);
  const syntaxTree = parse(tokens);
  syntaxTree.forEach(node => {
    // parse...
  });
}

function tokenize(code) {
  const REGEXES = [
    // ...
  ];

  const statements = code.split(" ");
  const tokens = [];
  REGEXES.forEach(REGEX => {
    statements.forEach(statement => {
      tokens.push(/* ... */);
    });
  });

  return tokens;
}

function parse(tokens) {
  const syntaxTree = [];
  tokens.forEach(token => {
    syntaxTree.push(/* ... */);
  });

  return syntaxTree;
}

5.刪除重複的代碼，抽離成函數

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 "manager":
        data.portfolio = employee.getMBAProjects();
        break;
      case "developer":
        data.githubLink = employee.getGithubLink();
        break;
    }

    render(data);
  });
}

6.使用Object.assign設置默認對象

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",
  // User did not include 'body' key
  buttonText: "Send",
  cancellable: true
};

function createMenu(config) {
  config = Object.assign(
    {
      title: "Foo",
      body: "Bar",
      buttonText: "Baz",
      cancellable: true
    },
    config
  );

  // config now equals: {title: "Order", body: "Bar", buttonText: "Send", cancellable: true}
  // ...
}

createMenu(menuConfig);

7.不要將標誌用作函數參數

Bad:

function createFile(name, temp) {
  if (temp) {
    fs.create(`./temp/${name}`);
  } else {
    fs.create(name);
  }
}

Good:

function createFile(name) {
  fs.create(name);
}

function createTempFile(name) {
  createFile(`./temp/${name}`);
}

8.建議不要寫全局函數

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));
  }
}

9.支持函數式編程而不是命令式編程

Bad:

const programmerOutput = [
  {
    name: "Uncle Bobby",
    linesOfCode: 500
  },
  {
    name: "Suzie Q",
    linesOfCode: 1500
  },
  {
    name: "Jimmy Gosling",
    linesOfCode: 150
  },
  {
    name: "Gracie Hopper",
    linesOfCode: 1000
  }
];

let totalOutput = 0;

for (let i = 0; i < programmerOutput.length; i++) {
  totalOutput += programmerOutput[i].linesOfCode;
}

Good:

const programmerOutput = [
  {
    name: "Uncle Bobby",
    linesOfCode: 500
  },
  {
    name: "Suzie Q",
    linesOfCode: 1500
  },
  {
    name: "Jimmy Gosling",
    linesOfCode: 150
  },
  {
    name: "Gracie Hopper",
    linesOfCode: 1000
  }
];

const totalOutput = programmerOutput.reduce(
  (totalLines, output) => totalLines + output.linesOfCode,
  0
);

10.將條件比較封裝成函數

Bad:

if (fsm.state === "fetching" && isEmpty(listNode)) {
  // ...
}

Good:

function shouldShowSpinner(fsm, listNode) {
  return fsm.state === "fetching" && isEmpty(listNode);
}

if (shouldShowSpinner(fsmInstance, listNodeInstance)) {
  // ...
}

11.避免負面比較

Bad:

function isDOMNodeNotPresent(node) {
  // ...
}

if (!isDOMNodeNotPresent(node)) {
  // ...
}

Good:

function isDOMNodePresent(node) {
  // ...
}

if (isDOMNodePresent(node)) {
  // ...
}

對象

1.使用getters和setters,避免直接修改對象的屬性

Bad:

function makeBankAccount() {
  // ...

  return {
    balance: 0
    // ...
  };
}

const account = makeBankAccount();
account.balance = 100;

Good:

function makeBankAccount() {
  // this one is private
  let balance = 0;

  // a "getter", made public via the returned object below
  function getBalance() {
    return balance;
  }

  // a "setter", made public via the returned object below
  function setBalance(amount) {
    // ... validate before updating the balance
    balance = amount;
  }

  return {
    // ...
    getBalance,
    setBalance
  };
}

const account = makeBankAccount();
account.setBalance(100);

2.使用對象的私有屬性

Bad:

const Employee = function(name) {
  this.name = name;
};

Employee.prototype.getName = function getName() {
  return this.name;
};

const employee = new Employee("John Doe");
console.log(`Employee name: ${employee.getName()}`); // Employee name: John Doe
delete employee.name;
console.log(`Employee name: ${employee.getName()}`); // Employee name: undefined

Good:

function makeEmployee(name) {
  return {
    getName() {
      return name;
    }
  };
}

const employee = makeEmployee("John Doe");
console.log(`Employee name: ${employee.getName()}`); // Employee name: John Doe
delete employee.name;
console.log(`Employee name: ${employee.getName()}`); // Employee name: John Doe