INTRO TO CLEAN CODE IN JS

THE JAVASCRIPT GUIDE TO

CLEAN

CODE

PRESENTED BY BIANCA GANDOLFO

VARIABLES

Use meaningful and pronounceable variable names.

Bad:

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

 

Good:

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

INTRO TO CLEAN CODE IN JS

Use the same vocabulary for the same type of variable

Bad:

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

 

Good:

getUser();

INTRO TO CLEAN CODE IN JS

VARIABLES

Use searchable names

Bad:

// What the heck is 86400000 for?
setTimeout(blastOff, 86400000);

 

Good:

// Declare them as capitalized `const` globals.
const MILLISECONDS_IN_A_DAY = 86400000;

setTimeout(blastOff, MILLISECONDS_IN_A_DAY);

 

We will read more code than we will ever write. It's important that the code we do write is readable and searchable. By notnaming variables that end up being meaningful for understanding our program, we hurt our readers.  Make your names searchable.

INTRO TO CLEAN CODE IN JS

VARIABLES

Use explanatory

variables

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);

INTRO TO CLEAN CODE IN JS

VARIABLES

Avoid Mental Mapping

Explicit is better than implicit.

Bad:

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

INTRO TO CLEAN CODE IN JS

VARIABLES

Avoid Mental Mapping

Good:

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

Explicit is better than implicit.

INTRO TO CLEAN CODE IN JS

VARIABLES

Don't add unneeded context

Good:

const Car = {
  make: 'Honda',
  model: 'Accord',
  color: 'Blue'
};

function paintCar(car) {
  car.color = 'Red';
}

If your class/object name tells you something, don't repeat that in your variable name.

Bad:

const Car = {
  carMake: 'Honda',
  carModel: 'Accord',
  carColor: 'Blue'
};

function paintCar(car) {
  car.carColor = 'Red';
}

INTRO TO CLEAN CODE IN JS

VARIABLES

Use default arguments instead of short circuiting or conditionals

Bad:

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

Good:

function createMicrobrewery(breweryName = 'Hipster Brew Co.') {
  // ...
}

INTRO TO CLEAN CODE IN JS

VARIABLES

Function arguments (2 or fewer ideally)

Bad:

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

INTRO TO CLEAN CODE IN JS

FUNCTIONS

Function arguments (2 or fewer ideally)

Good:

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

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

 

INTRO TO CLEAN CODE IN JS

FUNCTIONS

FUNCTIONS SHOULD DO ONE THING

This is by far the most important rule in software engineering. When functions do more than one thing, they are harder to compose, test, and reason about. When you can isolate a function to just one action, they can be refactored easily and your code will read much cleaner. If you take nothing else away from this guide other than this, you'll be ahead of many developers.

FUNCTIONS

INTRO TO CLEAN CODE IN JS

Function names should say what they do

Bad:

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

const date = new Date();

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

Good:

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

const date = new Date();
addMonthToDate(date, 1);

INTRO TO CLEAN CODE IN JS

FUNCTIONS

Bad:

function emailClients(clients) {
  clients.forEach((client) => {
    const clientRecord = database.lookup(client);
    if (clientRecord.isActive()) {
      email(client);
    }
  });
}

INTRO TO CLEAN CODE IN JS

FUNCTIONS

Good:

function emailClients(clients) {
  clients
    .filter(isClientActive)
    .forEach(email);
}

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

INTRO TO CLEAN CODE IN JS

FUNCTIONS

FUNCTIONS SHOULD ONLY

BE ONE LEVEL OF ABSTRACTION

When you have more than one level of abstraction your function is usually doing too much. Splitting up functions leads to reusability and easier testing.

FUNCTIONS

INTRO TO CLEAN CODE IN JS

FUNCTIONS

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...
  });
}

INTRO TO CLEAN CODE IN JS

FUNCTIONS

INTRO TO CLEAN CODE IN JS

Good:

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

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

  return tokens;
}
 
function lexer(tokens) {
  const ast = [];
  tokens.forEach((token) => {
    ast.push( /* ... */ );
  });

  return ast;
}

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

Remove duplicate code

Do your absolute best to avoid duplicate code. Duplicate code is bad because it means that there's more than one place to alter something if you need to change some logic.

INTRO TO CLEAN CODE IN JS

FUNCTIONS

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);
  });
}


INTRO TO CLEAN CODE IN JS

FUNCTIONS

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);
  });
}

INTRO TO CLEAN CODE IN JS

FUNCTIONS

Good:

function showList(employees) {
  employees.forEach((employee) => {
    const expectedSalary = employee.calculateExpectedSalary();
    const experience = employee.getExperience();

    let portfolio = employee.getGithubLink();

    if (employee.type === 'manager') {
      portfolio = employee.getMBAProjects();
    }

    const data = {
      expectedSalary,
      experience,
      portfolio
    };

    render(data);
  });
}

Set default objects with Objects.assign

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);

INTRO TO CLEAN CODE IN JS

FUNCTIONS

Set default objects with Objects.assign

INTRO TO CLEAN CODE IN JS

FUNCTIONS

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);

A DON'T USE FLAGS

AS FUNCTION PARAMETERS

FUNCTIONS

Flags tell your user that this function does more than one thing. Functions should do one thing. Split out your functions if they are following different code paths based on a boolean.

INTRO TO CLEAN CODE IN JS

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}`);
}

INTRO TO CLEAN CODE IN JS

FUNCTIONS

AVOID SIDE EFFECTS (PART 1)

FUNCTIONS

A function produces a side effect if it does anything other than take a value in and return another value or values. A side effect could be writing to a file, modifying some global variable, or accidentally wiring all your money to a stranger.

INTRO TO CLEAN CODE IN JS

Bad:

// Global variable referenced by following function.
// If we had another function that used this name, now it'd be an array and it could break it.
let name = 'Ryan McDermott';

function splitIntoFirstAndLastName() {
  name = name.split(' ');
}

splitIntoFirstAndLastName();

console.log(name); // ['Ryan', 'McDermott'];

 

Good:

function splitIntoFirstAndLastName(name) {
  return name.split(' ');
}

const name = 'Ryan McDermott';
const newName = splitIntoFirstAndLastName(name);

console.log(name); // 'Ryan McDermott';
console.log(newName); // ['Ryan', 'McDermott'];

INTRO TO CLEAN CODE IN JS

FUNCTIONS

AVOID SIDE EFFECTS (PART 2)

FUNCTIONS

In JavaScript, primitives are passed by value and objects/arrays are passed by reference. In the case of objects and arrays, if our function makes a change in a shopping cart array, for example, by adding an item to purchase, then any other function that uses that cart array will be affected by this addition. That may be great, however, it can be bad too.

INTRO TO CLEAN CODE IN JS

Bad:

const addItemToCart = (cart, item) => {
  cart.push({ item, date: Date.now() });
};

 

Good:

const addItemToCart = (cart, item) => {
  return [...cart, { item, date : Date.now() }];
};

 

INTRO TO CLEAN CODE IN JS

FUNCTIONS

DON'T WRITE

GLOBAL FUNCTIONS

FUNCTIONS

Polluting globals is a bad practice in JavaScript because you could clash with another library and the user of your API would be none-the-wiser until they get an exception in production.  

INTRO TO CLEAN CODE IN JS

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));
  }
}

INTRO TO CLEAN CODE IN JS

FUNCTIONS

FUNCTIONS

Favor functional programming over imperative programming

JavaScript isn't a functional language in the way that Haskell is, but it has a functional flavor to it. Functional languages are cleaner and easier to test. Favor this style of programming when you can.

INTRO TO CLEAN CODE IN JS

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;
}

INTRO TO CLEAN CODE IN JS

FUNCTIONS

Good:

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

const INITIAL_VALUE = 0;

const totalOutput = programmerOutput
  .map((programmer) => programmer.linesOfCode)
  .reduce((acc, linesOfCode) => acc + linesOfCode, INITIAL_VALUE);

 

INTRO TO CLEAN CODE IN JS

FUNCTIONS

Encapsulate conditionals

Bad:

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

 

Good:

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

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

INTRO TO CLEAN CODE IN JS

FUNCTIONS

Avoid negative conditionals

Bad:

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

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


Good:

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

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

INTRO TO CLEAN CODE IN JS

FUNCTIONS

AVOID CONDITIONALS

FUNCTIONS

A function should only do one thing. When you have classes and functions that have if statements, you are telling your user that your function does more than one thing. Remember, just do one thing.

INTRO TO CLEAN CODE IN JS

Bad:

class Airplane {
  // ...
  getCruisingAltitude() {
    switch (this.type) {
      case '777':
        return this.getMaxAltitude() - this.getPassengerCount();
      case 'Air Force One':
        return this.getMaxAltitude();
      case 'Cessna':
        return this.getMaxAltitude() - this.getFuelExpenditure();
    }
  }
}

INTRO TO CLEAN CODE IN JS

FUNCTIONS

Good:

class Airplane {
  // ...
}

class Boeing777 extends Airplane {
  // ...
  getCruisingAltitude() {
    return this.getMaxAltitude() - this.getPassengerCount();
  }
}

class AirForceOne extends Airplane {
  // ...
  getCruisingAltitude() {
    return this.getMaxAltitude();
  }
}
class Cessna extends Airplane {
  // ...
  getCruisingAltitude() {
    return this.getMaxAltitude() - this.getFuelExpenditure();
  }
}

INTRO TO CLEAN CODE IN JS

FUNCTIONS

AVOID TYPE-CHECKING (PART 1)

FUNCTIONS

JavaScript is untyped, which means your functions can take any type of argument. Sometimes you are bitten by this freedom and it becomes tempting to do type-checking in your functions. There are many ways to avoid having to do this. The first thing to consider is consistent APIs.

INTRO TO CLEAN CODE IN JS

Bad:

function travelToTexas(vehicle) {
  if (vehicle instanceof Bicycle) {
    vehicle.pedal(this.currentLocation, new Location('texas'));
  } else if (vehicle instanceof Car) {
    vehicle.drive(this.currentLocation, new Location('texas'));
  }
}

 

Good:

function travelToTexas(vehicle) {
  vehicle.move(this.currentLocation, new Location('texas'));
}

PRESENTED BY BIANCA GANDOLFO

INTRO TO CLEAN CODE IN JS

FUNCTIONS

AVOID TYPE-CHECKING (PART 2)

FUNCTIONS

If you are working with basic primitive values like strings, integers, and arrays, and you can't use polymorphism but you still feel the need to type-check, you should consider using TypeScript. It is an excellent alternative to normal JavaScript, as it provides you with static typing on top of standard JavaScript syntax. The problem with manually type-checking normal  is that doing it well requires so much extra verbiage that the faux "type-safety" you get doesn't make up for the lost readability. Keep your JavaScript clean, write good tests, and have good code reviews.

INTRO TO CLEAN CODE IN JS

Bad:

function combine(val1, val2) {
  if (typeof val1 === 'number' && typeof val2 === 'number' ||
      typeof val1 === 'string' && typeof val2 === 'string') {
    return val1 + val2;
  }

  throw new Error('Must be of type String or Number');
}

 

Good:

function combine(val1, val2) {
  return val1 + val2;
}

INTRO TO CLEAN CODE IN JS

FUNCTIONS

DON'T OVER-OPTIMIZE

FUNCTIONS

Modern browsers do a lot of optimization under-the-hood at runtime. A lot of times, if you are optimizing then you are just wasting your time. There are good resources for seeing where optimization is lacking. Target those in the meantime, until they are fixed if they can be.

INTRO TO CLEAN CODE IN JS

Bad:

// On old browsers, each iteration with uncached `list.length` would be costly
// because of `list.length` recomputation. In modern browsers, this is optimized.
for (let i = 0, len = list.length; i < len; i++) {
  // ...
}

 

Good:

for (let i = 0; i < list.length; i++) {
  // ...
}

INTRO TO CLEAN CODE IN JS

FUNCTIONS

REMOVE DEAD CODE

Dead code is just as bad as duplicate code. There's no reason to keep it in your codebase. If it's not being called, get rid of it! It will still be safe in your version history if you still need it.

INTRO TO CLEAN CODE IN JS

FUNCTIONS

Bad:

function oldRequestModule(url) {
  // ...
}

function newRequestModule(url) {
  // ...
}

const req = newRequestModule;
inventoryTracker('apples', req, 'www.inventory-awesome.io');


Good:

function newRequestModule(url) {
  // ...
}

const req = newRequestModule;
inventoryTracker('apples', req, 'www.inventory-awesome.io');

INTRO TO CLEAN CODE IN JS

FUNCTIONS

USE GETTERS AND SETTERS

OBJECTS AND DATA STRUCTURES

JavaScript doesn't have interfaces or types so it is very hard to enforce this pattern, because we don't have keywords like public and private. As it is. using getters and setters to access data on objects is far better than simply looking for a property on an object. "Why?" you might ask. Well, here's an unorganized list of reasons why.

  • When you want to do more beyond getting an object property, you don't have to look up and change every accessor in your codebase.
  • Makes adding validation simple when doing a set.
  • Encapsulates the internal representation.
  • Easy to add logging and error handling when getting and setting.
  • Inheriting this class, you can override default functionality.
  • You can lazy load your object's properties, let's say getting it from a server.

INTRO TO CLEAN CODE IN JS

Bad:

class BankAccount {
  constructor() {
    this.balance = 1000;
  }
}

const bankAccount = new BankAccount();

// Buy shoes...
bankAccount.balance -= 100;

INTRO TO CLEAN CODE IN JS

OBJECTS AND DATA STRUCTURES

Good:

class BankAccount {
  constructor(balance = 1000) {
    this._balance = balance;
  }

  // It doesn't have to be prefixed with `get` or `set` to be a getter/setter
  set balance(amount) {
    if (this.verifyIfAmountCanBeSetted(amount)) {
      this._balance = amount;
    }
  }

  get balance() {
    return this._balance;
  }

  verifyIfAmountCanBeSetted(val) {
    // ...
  }
}

INTRO TO CLEAN CODE IN JS

OBJECTS AND DATA STRUCTURES

const bankAccount = new BankAccount();

// Buy shoes...
bankAccount.balance -= shoesPrice;

// Get balance
let balance = bankAccount.balance;

Make objects have private members

This can be accomplished through closures.

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

OBJECTS AND DATA STRUCTURES

INTRO TO CLEAN CODE IN JS

Make objects have private members

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

This can be accomplished through closures.

OBJECTS AND DATA STRUCTURES

INTRO TO CLEAN CODE IN JS

SINGLE RESPONSIBILITY PRINCIPLE (SRP)

CLASSES

AS stated in Clean Code, "There should never be more than one reason for a class to change".  It's tempting to jam-pack a class with a lot of functionality, like when you can only take one suitcase on your flight. The issue with this is that your class won't be conceptually cohesive and it will give it many reasons to change. Minimizing the amount of times you need to change a class is important. It's important because if too much functionality is in one class and you modify a piece of it, it can be difficult to understand how that will affect other dependent modules in your codebase.  

INTRO TO CLEAN CODE IN JS

Good:

class UserAuth {
  constructor(user) {
    this.user = user;
  }

  verifyCredentials() {
    // ...
  }
}


class UserSettings {
  constructor(user) {
    this.user = user;
    this.auth = new UserAuth(user);
  }

  changeSettings(settings) {
    if (this.auth.verifyCredentials()) {
      // ...
    }
  }
}

Bad:

class UserSettings {
  constructor(user) {
    this.user = user;
  }

  changeSettings(settings) {
    if (this.verifyCredentials()) {
      // ...
    }
  }

  verifyCredentials() {
    // ...
  }
}

CLASSES

INTRO TO CLEAN CODE IN JS

OPEN / CLOSED PRINCIPLE (OCP)

CLASSES

As stated by Bertrand Meyer, "software entities (classes, modules, functions, etc.) should be open for extension, but closed for modification." What does that mean though? This principle basically states that you should allow users to add new functionalities without changing existing code.

INTRO TO CLEAN CODE IN JS

  fetch(url) {
    if (this.adapter.name === 'ajaxAdapter') {
      return makeAjaxCall(url).then((response) => {
        // transform response and return
      });
    } else if (this.adapter.name === 'httpNodeAdapter') {
      return makeHttpCall(url).then((response) => {
        // transform response and return
      });
    }
  }
}

function makeAjaxCall(url) {
  // request and return promise
}

function makeHttpCall(url) {
  // request and return promise
}

Bad:

class AjaxAdapter extends Adapter {
  constructor() {
    super();
    this.name = 'ajaxAdapter';
  }
}

class NodeAdapter extends Adapter {
  constructor() {
    super();
    this.name = 'nodeAdapter';
  }
}

class HttpRequester {
  constructor(adapter) {
    this.adapter = adapter;
  }


INTRO TO CLEAN CODE IN JS

CLASSES

class HttpRequester {
  constructor(adapter) {
    this.adapter = adapter;
  }

  fetch(url) {
    return this.adapter.request(url).then((response) => {
      // transform response and return
    });
  }
}

Good:

class AjaxAdapter extends Adapter {
  constructor() {
    super();
    this.name = 'ajaxAdapter';
  }

  request(url) {
    // request and return promise
  }
}

class NodeAdapter extends Adapter {
  constructor() {
    super();
    this.name = 'nodeAdapter';
  }

  request(url) {
    // request and return promise
  }
}

INTRO TO CLEAN CODE IN JS

CLASSES

THE LISKOV SUBSTITUTION PRINCIPLE (LSP)

CLASSES

This is a scary term for a very simple concept. It's formally defined as "If S is a subtype of T, then objects of type T may be replaced with objects of type S (i.e., objects of type S may substitute objects of type T) without altering any of the desirable properties of that program (correctness, task performed, etc.)." That's an even scarier definition.

The best explanation for this is if you have a parent class and a child class, then the base class and child class can be used interchangeably without getting incorrect results. This might still be confusing, so let's take a look at the classic Square-Rectangle example. Mathematically, a square is a rectangle, but if you model it using the "is-a" relationship via inheritance, you quickly get into trouble.

INTRO TO CLEAN CODE IN JS

class Square extends Rectangle {
  setWidth(width) {
    this.width = width;
    this.height = width;
  }

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

function renderLargeRectangles(rectangles) {
  rectangles.forEach((rectangle) => {
    rectangle.setWidth(4);
    rectangle.setHeight(5);
    const area = rectangle.getArea(); // BAD: Will return 25 for Square. Should be 20.
    rectangle.render(area);
  });
}

const rectangles = [new Rectangle(), new Rectangle(), new Square()];
renderLargeRectangles(rectangles)

Bad:

class Rectangle {
  constructor() {
    this.width = 0;
    this.height = 0;
  }

  setColor(color) {
    // ...
  }

  render(area) {
    // ...
  }

  setWidth(width) {
    this.width = width;
  }

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

  getArea() {
    return this.width * this.height;
  }
}

CLASSES

INTRO TO CLEAN CODE IN JS

class Square extends Shape {
  constructor() {
    super();
    this.length = 0;
  }

  setLength(length) {
    this.length = length;
  }

  getArea() {
    return this.length * this.length;
  }
}
function renderLargeShapes(shapes) {
  shapes.forEach((shape) => {
    switch (shape.constructor.name) {
      case 'Square':
        shape.setLength(5);
        break;
      case 'Rectangle':
        shape.setWidth(4);
        shape.setHeight(5);
    }

    const area = shape.getArea();
    shape.render(area);
  });
}

const shapes = [new Rectangle(), new Rectangle(), new Square()];
renderLargeShapes(shapes);

Good:

class Shape {
  setColor(color) {
    // ...
  }

  render(area) {
    // ...
  }
}

class Rectangle extends Shape {
  constructor() {
    super();
    this.width = 0;
    this.height = 0;
  }

  setWidth(width) {
    this.width = width;
  }

  setHeight(height) {
    this.height = height;
  }​​​
 getArea() {
    return this.width * this.height;
  }
}

CLASSES

INTRO TO CLEAN CODE IN JS

INTERFACE SEGREGATION PRINCIPLE (ISP)

CLASSES

JavaScript doesn't have interfaces so this principle doesn't apply as strictly as others. However, it's important and relevant even with JavaScript's lack of type system.

ISP states that "Clients should not be forced to depend upon interfaces that they do not use." Interfaces are implicit contracts in JavaScript because of duck typing.

A good example to look at that demonstrates this principle in JavaScript is for classes that require large settings objects. Not requiring clients to setup huge amounts of options is beneficial, because most of the time they won't need all of the settings. Making them optional helps prevent having a "fat interface".

INTRO TO CLEAN CODE IN JS

Bad:

class DOMTraverser {
  constructor(settings) {
    this.settings = settings;
    this.setup();
  }

  setup() {
    this.rootNode = this.settings.rootNode;
    this.animationModule.setup();
  }

  traverse() {
    // ...
  }
}

const $ = new DOMTraverser({
  rootNode: document.getElementsByTagName('body'),
  animationModule() {} // Most of the time, we won't need to animate when traversing.
  // ...
});

CLASSES

INTRO TO CLEAN CODE IN JS

Good:

class DOMTraverser {
  constructor(settings) {
    this.settings = settings;
    this.options = settings.options;
    this.setup();
  }

  setup() {
    this.rootNode = this.settings.rootNode;
    this.setupOptions();
  }

  setupOptions() {
    if (this.options.animationModule) {
      // ...
    }
  }

  traverse() {
    // ...
  }
}

CLASSES

INTRO TO CLEAN CODE IN JS

const $ = new DOMTraverser({
  rootNode: document.getElementsByTagName('body'),
  options: {
    animationModule() {}
  }
});

DEPENDENCY INVERSION PRINCIPLE (DIP)

CLASSES

This principle states two essential things:

1. High-level modules should not depend on low-level modules. Both should depend on abstractions.

2. Abstractions should not depend upon details. Details should depend on abstractions.

INTRO TO CLEAN CODE IN JS

Good:

class InventoryTracker {
  constructor(items, requester) {
    this.items = items;
    this.requester = requester;
  }

  requestItems() {
    this.items.forEach((item) => {
      this.requester.requestItem(item);
    });
  }
}

class InventoryRequesterV1 {
  constructor() {
    this.REQ_METHODS = ['HTTP'];
  }

  requestItem(item) {
    // ...
  }
}

INTRO TO CLEAN CODE IN JS

CLASSES

class InventoryRequesterV2 {
  constructor() {
    this.REQ_METHODS = ['WS'];
  }

  requestItem(item) {
    // ...
  }
}

// By constructing our dependencies externally and injecting them, we can easily
// substitute our request module for a fancy new one that uses WebSockets.
const inventoryTracker = new InventoryTracker(['apples', 'bananas'], new InventoryRequesterV2());
inventoryTracker.requestItems();

INTRO TO CLEAN CODE IN JS

CLASSES

Bad:

class InventoryRequester {
  constructor() {
    this.REQ_METHODS = ['HTTP'];
  }

  requestItem(item) {
    // ...
  }
}

class InventoryTracker {
  constructor(items) {
    this.items = items;

    // BAD: We have created a dependency on a specific request implementation.
    // We should just have requestItems depend on a request method: `request`
    this.requester = new InventoryRequester();
  }

INTRO TO CLEAN CODE IN JS

CLASSES

INTRO TO CLEAN CODE IN JS

CLASSES

  requestItems() {
    this.items.forEach((item) => {
      this.requester.requestItem(item);
    });
  }
}

const inventoryTracker = new InventoryTracker(['apples', 'bananas']);
inventoryTracker.requestItems();

Prefer ES2015/ES6 classes over ES5 plain functions

CLASSES

It's very difficult to get readable class inheritance, construction, and method definitions for classical ES5 classes. If you need inheritance (and be aware that you might not), then prefer classes. However, prefer small functions over classes until you find yourself needing larger and more complex objects.

INTRO TO CLEAN CODE IN JS

Bad:

const Animal = function(age) {
  if (!(this instanceof Animal)) {
    throw new Error('Instantiate Animal with `new`');
  }

  this.age = age;
};

Animal.prototype.move = function move() {};

const Mammal = function(age, furColor) {
  if (!(this instanceof Mammal)) {
    throw new Error('Instantiate Mammal with `new`');
  }

  Animal.call(this, age);
  this.furColor = furColor;
};

CLASSES

Mammal.prototype = Object.create(Animal.prototype);
Mammal.prototype.constructor = Mammal;
Mammal.prototype.liveBirth = function liveBirth() {};

const Human = function(age, furColor, languageSpoken) {
  if (!(this instanceof Human)) {
    throw new Error('Instantiate Human with `new`');
  }

  Mammal.call(this, age, furColor);
  this.languageSpoken = languageSpoken;
};

Human.prototype = Object.create(Mammal.prototype);
Human.prototype.constructor = Human;
Human.prototype.speak = function speak() {};

INTRO TO CLEAN CODE IN JS

Good:

class Animal {
  constructor(age) {
    this.age = age;
  }

  move() { /* ... */ }
}

class Mammal extends Animal {
  constructor(age, furColor) {
    super(age);
    this.furColor = furColor;
  }

  liveBirth() { /* ... */ }
}


INTRO TO CLEAN CODE IN JS

CLASSES

class Human extends Mammal {
  constructor(age, furColor, languageSpoken) {
    super(age, furColor);
    this.languageSpoken = languageSpoken;
  }

  speak() { /* ... */ }
}

Use method chaining

CLASSES

This pattern is very useful in JavaScript and you see it in many libraries such as jQuery and Lodash. It allows your code to be expressive, and less verbose. For that reason, I say, use method chaining and take a look at how clean your code will be. In your class functions, simply return this at the end of every function, and you can chain further class methods onto it.

INTRO TO CLEAN CODE IN JS

Bad:

class Car {
  constructor() {
    this.make = 'Honda';
    this.model = 'Accord';
    this.color = 'white';
  }

  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();
car.setColor('pink');
car.setMake('Ford');
car.setModel('F-150');
car.save();

INTRO TO CLEAN CODE IN JS

CLASSES

Good:

class Car {
  constructor() {
    this.make = 'Honda';
    this.model = 'Accord';
    this.color = 'white';
  }

  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()
  .setColor('pink')
  .setMake('Ford')
  .setModel('F-150')
  .save();

INTRO TO CLEAN CODE IN JS

CLASSES

Prefer composition over inheritance

CLASSES

There are lots of good reasons to use inheritance and lots of good reasons to use composition. The main point for this maxim is that if your mind instinctively goes for inheritance, try to think if composition could model your problem better. In some cases it can.

This is a decent list of when inheritance makes more sense than composition:

1. Your inheritance represents an "is-a" relationship and not a "has-a" relationship (Human->Animal vs. User->UserDetails).

2. You can reuse code from the base classes (Humans can move like all animals).

3. You want to make global changes to derived classes by changing a base class. (Change the caloric expenditure of all animals when they move).

INTRO TO CLEAN CODE IN JS

Bad:

class Employee {
  constructor(name, email) {
    this.name = name;
    this.email = email;
  }

  // ...
}

// Bad because Employees "have" tax data. EmployeeTaxData is not a type of Employee
class EmployeeTaxData extends Employee {
  constructor(ssn, salary) {
    super();
    this.ssn = ssn;
    this.salary = salary;
  }

  // ...
}

INTRO TO CLEAN CODE IN JS

CLASSES

INTRO TO CLEAN CODE IN JS

CLASSES

Good:

class EmployeeTaxData {
  constructor(ssn, salary) {
    this.ssn = ssn;
    this.salary = salary;
  }

  // ...
}

class Employee {
  constructor(name, email) {
    this.name = name;
    this.email = email;
  }

  setTaxData(ssn, salary) {
    this.taxData = new EmployeeTaxData(ssn, salary);
  }
  // ...
}

TESTING

Testing is more important than shipping. If you have no tests or an inadequate amount, then every time you ship code you won't be sure that you didn't break anything. Deciding on what constitutes an adequate amount is up to your team, but having 100% coverage (all statements and branches) is how you achieve very high confidence and developer peace of mind. This means that in addition to having a great testing framework, you also need to use a good coverage tool.

INTRO TO CLEAN CODE IN JS

Bad:

const assert = require('assert');

describe('MakeMomentJSGreatAgain', () => {
  it('handles date boundaries', () => {
    let date;

    date = new MakeMomentJSGreatAgain('1/1/2015');
    date.addDays(30);
    date.shouldEqual('1/31/2015');

    date = new MakeMomentJSGreatAgain('2/1/2016');
    date.addDays(28);
    assert.equal('02/29/2016', date);

    date = new MakeMomentJSGreatAgain('2/1/2015');
    date.addDays(28);
    assert.equal('03/01/2015', date);
  });
});

SINGLE CONCEPT TEST

INTRO TO CLEAN CODE IN JS

SINGLE CONCEPT TEST

INTRO TO CLEAN CODE IN JS

Good:

const assert = require('assert');

describe('MakeMomentJSGreatAgain', () => {
  it('handles 30-day months', () => {
    const date = new MakeMomentJSGreatAgain('1/1/2015');
    date.addDays(30);
    date.shouldEqual('1/31/2015');
  });

  it('handles leap year', () => {
    const date = new MakeMomentJSGreatAgain('2/1/2016');
    date.addDays(28);
    assert.equal('02/29/2016', date);
  });

  it('handles non-leap year', () => {
    const date = new MakeMomentJSGreatAgain('2/1/2015');
    date.addDays(28);
    assert.equal('03/01/2015', date);
  });
});

 

Use promises

not callbacks.

CONCURRENCY

Callbacks aren't clean, and they cause excessive amounts of nesting. With ES2015/ES6, Promises are a built-in global type. Use them!

INTRO TO CLEAN CODE IN JS

Bad:

require('request').get('https://en.wikipedia.org/wiki/Robert_Cecil_Martin', (requestErr, response) => {
  if (requestErr) {
    console.error(requestErr);
  } else {
    require('fs').writeFile('article.html', response.body, (writeErr) => {
      if (writeErr) {
        console.error(writeErr);
      } else {
        console.log('File written');
      }
    });
  }
});

CONCURRENCY

INTRO TO CLEAN CODE IN JS

CONCURRENCY

Good:

require('request-promise').get('https://en.wikipedia.org/wiki/Robert_Cecil_Martin')
  .then((response) => {
    return require('fs-promise').writeFile('article.html', response);
  })
  .then(() => {
    console.log('File written');
  })
  .catch((err) => {
    console.error(err);
  });

INTRO TO CLEAN CODE IN JS

Async/Await are even cleaner than Promises.

CONCURRENCY

Promises are a very clean alternative to callbacks, but ES2017/ES8 brings async and await which offer an even cleaner solution. All you need is a function that is prefixed in an async keyword, and then you can write your logic imperatively without a then chain of functions. Use this if you can take advantage of ES2017/ES8 features today!

INTRO TO CLEAN CODE IN JS

Bad:

require('request-promise').get('https://en.wikipedia.org/wiki/Robert_Cecil_Martin')
  .then((response) => {
    return require('fs-promise').writeFile('article.html', response);
  })
  .then(() => {
    console.log('File written');
  })
  .catch((err) => {
    console.error(err);
  });

 

 

CONCURRENCY

INTRO TO CLEAN CODE IN JS

Good:

async function getCleanCodeArticle() {
  try {
    const response = await require('request-promise').get('https://en.wikipedia.org/wiki/Robert_Cecil_Martin');
    await require('fs-promise').writeFile('article.html', response);
    console.log('File written');
  } catch(err) {
    console.error(err);
  }
}

CONCURRENCY

INTRO TO CLEAN CODE IN JS

ERROR HANDLING

Thrown errors are a good thing! They mean the runtime has successfully identified when something in your program has gone wrong and it's letting you know by stopping function execution on the current stack, killing the process (in Node), and notifying you in the console with a stack trace.

DON'T IGNORE CAUGHT ERRORS

Doing nothing with a caught error doesn't give you the ability to ever fix or react to said error. Logging the error to the console (console.log) isn't much better as often times it can get lost in a sea of things printed to the console. If you wrap any bit of code in a try/catch it means you think an error may occur there and therefore you should have a plan, or create a code path, for when it occurs.

INTRO TO CLEAN CODE IN JS

Bad:

try {
  functionThatMightThrow();
} catch (error) {
  console.log(error);
}

 

Good:

try {
  functionThatMightThrow();
} catch (error) {
  // One option (more noisy than console.log):
  console.error(error);
  // Another option:
  notifyUserOfError(error);
  // Another option:
  reportErrorToService(error);
  // OR do all three!
}

INTRO TO CLEAN CODE IN JS

ERROR HANDLING

Don't ignore rejected promises

For the same reason you shouldn't ignore caught errors from try/catch.

ERROR HANDLING

Bad:

getdata()
.then((data) => {
  functionThatMightThrow(data);
})
.catch((error) => {
  console.log(error);
});

Good:

getdata()
.then((data) => {
  functionThatMightThrow(data);
})
.catch((error) => {
  // One option (more noisy than console.log):
  console.error(error);
  // Another option:
  notifyUserOfError(error);
  // Another option:
  reportErrorToService(error);
  // OR do all three!
});

INTRO TO CLEAN CODE IN JS

Formatting is subjective. Like many rules herein, there is no hard and fast rule that you must follow. The main point is DO NOT ARGUE over formatting. There are tons of tools to automate this. Use one!

For things that don't fall under the purview of automatic formatting (indentation, tabs vs. spaces, double vs. single quotes, etc.) look here for some guidance.

FORMATTING

Use consistent capitalization

JavaScript is untyped, so capitalization tells you a lot about your variables, functions, etc. These rules are subjective, so your team can choose whatever they want. The point is, no matter what you all choose, just be consistent.

INTRO TO CLEAN CODE IN JS

FORMATTING

Bad:

const DAYS_IN_WEEK = 7;
const daysInMonth = 30;

const songs = ['Back In Black', 'Stairway to Heaven', 'Hey Jude'];
const Artists = ['ACDC', 'Led Zeppelin', 'The Beatles'];

function eraseDatabase() {}
function restore_database() {}

class animal {}
class Alpaca {}

 

Good:

const DAYS_IN_WEEK = 7;
const DAYS_IN_MONTH = 30;

const songs = ['Back In Black', 'Stairway to Heaven', 'Hey Jude'];
const artists = ['ACDC', 'Led Zeppelin', 'The Beatles'];

function eraseDatabase() {}
function restoreDatabase() {}

class Animal {}
class Alpaca {}

INTRO TO CLEAN CODE IN JS

FORMATTING

Good:

const DAYS_IN_WEEK = 7;
const DAYS_IN_MONTH = 30;

const songs = ['Back In Black', 'Stairway to Heaven', 'Hey Jude'];
const artists = ['ACDC', 'Led Zeppelin', 'The Beatles'];

function eraseDatabase() {}
function restoreDatabase() {}

class Animal {}
class Alpaca {}

INTRO TO CLEAN CODE IN JS

FUNCTION CALLERS AND CALLEES SHOULD BE CLOSE

FORMATTING

If a function calls another, keep those functions vertically close in the source file. Ideally, keep the caller right above the callee. We tend to read code from top-to-bottom, like a newspaper. Because of this, make your code read that way.

INTRO TO CLEAN CODE IN JS

FORMATTING

Bad:

class PerformanceReview {
  constructor(employee) {
    this.employee = employee;
  }

  lookupPeers() {
    return db.lookup(this.employee, 'peers');
  }

  lookupManager() {
    return db.lookup(this.employee, 'manager');
  }

  getPeerReviews() {
    const peers = this.lookupPeers();
    // ...
  }

  perfReview() {
    this.getPeerReviews();
    this.getManagerReview();
    this.getSelfReview();
  }
  getManagerReview() {
    const manager = this.lookupManager();
  }

  getSelfReview() {
    // ...
  }
}

const review = new PerformanceReview(user);
review.perfReview();

INTRO TO CLEAN CODE IN JS

Good:

class PerformanceReview {
  constructor(employee) {
    this.employee = employee;
  }

  perfReview() {
    this.getPeerReviews();
    this.getManagerReview();
    this.getSelfReview();
  }

  getPeerReviews() {
    const peers = this.lookupPeers();
    // ...
  }

  lookupPeers() {
    return db.lookup(this.employee, 'peers');
  }

  getManagerReview() {
    const manager = this.lookupManager();
  }
  lookupManager() {
    return db.lookup(this.employee, 'manager');
  }

  getSelfReview() {
    // ...
  }
}

const review = new PerformanceReview(employee);
review.perfReview();

INTRO TO CLEAN CODE IN JS

FORMATTING

Only comment things that has business logic complexity.

Comments are an apology, not a requirement. Good codes mostly documents itself.  

COMMENTS

Bad:

function hashIt(data) {
  // The hash
  let hash = 0;

  // Length of string
  const length = data.length;

  // Loop through every character in data
  for (let i = 0; i < length; i++) {
    // Get character code.
    const char = data.charCodeAt(i);
    // Make the hash
    hash = ((hash << 5) - hash) + char;
    // Convert to 32-bit integer
    hash &= hash;
  }
}

Good:

function hashIt(data) {
  let hash = 0;
  const length = data.length;

  for (let i = 0; i < length; i++) {
    const char = data.charCodeAt(i);
    hash = ((hash << 5) - hash) + char;

    // Convert to 32-bit integer
    hash &= hash;
  }
}

PRESENTED BY BIANCA GANDOLFO

INTRO TO CLEAN CODE IN JS

Don't leave commented out code in your codebase

Version control exists for a reason. Leave old code in your history.

Bad:

doStuff();
// doOtherStuff();
// doSomeMoreStuff();
// doSoMuchStuff();

Good:

doStuff();

INTRO TO CLEAN CODE IN JS

COMMENTS

Don't have journal comments.

Remember, use version control! There's no need for dead code, commented code, and especially journal comments. Use git log to get history!

Bad:

/**
 * 2016-12-20: Removed monads, didn't understand them (RM)
 * 2016-10-01: Improved using special monads (JP)
 * 2016-02-03: Removed type-checking (LI)
 * 2015-03-14: Added combine with type-checking (JR)
 */
function combine(a, b) {
  return a + b;
}

Good:

function combine(a, b) {
  return a + b;
}

INTRO TO CLEAN CODE IN JS

COMMENTS

Avoid positional markers

They usually just add noise. Let the functions and variable names along with the proper indentation and formatting give the visual structure to your code.

Bad:

///////////////////////////////////////
// Scope Model Instantiation
///////////////////////////////////////
$scope.model = {
  menu: 'foo',
  nav: 'bar'
};

///////////////////////////////////////
// Action setup
///////////////////////////////////////
const actions = function() {
  // ...
};

 

Good:

$scope.model = {
  menu: 'foo',
  nav: 'bar'
};

const actions = function() {
  // ...
};

 

INTRO TO CLEAN CODE IN JS

COMMENTS

INTRO TO CLEAN CODE IN JS

THANK

YOU!

BIANCA GANDOLFO

INTRO TO CLEAN CODE IN JS

Clean Code

By Bianca Gandolfo

Clean Code

Clean Code in JS

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