clean-code-typescript

Clean Code concepts adapted for TypeScript.
Inspired from clean-code-javascript

Table of Contents

1. Introduction
2. Variables
3. Functions
4. Objects and Data Structures
5. Classes
6. SOLID
7. Testing
8. Concurrency
9. Error Handling
10. Formatting
11. Comments

Introduction

Software engineering principles, from Robert C. Martin's book Clean Code, adapted for TypeScript. This is not a style guide. It's a guide to producing readable, reusable, and refactorable software in TypeScript.

Not every principle herein has to be strictly followed, and even fewer will be universally agreed upon. These are guidelines and nothing more, but they are ones codified over many years of collective experience by the authors of Clean Code.

Our craft of software engineering is just a bit over 50 years old, and we are still learning a lot. When software architecture is as old as architecture itself, maybe then we will have harder rules to follow. For now, let these guidelines serve as a touchstone by which to assess the quality of the JavaScript code that you and your team produce.

One more thing: knowing these won't immediately make you a better software developer, and working with them for many years doesn't mean you won't make mistakes. Every piece of code starts as a first draft, like wet clay getting shaped into its final form. Finally, we chisel away the imperfections when we review it with our peers. Don't beat yourself up for first drafts that need improvement. Beat up the code instead!

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Variables

Use meaningful variable names

Distinguish names in such a way that the reader knows what the differences offer.

Bad:

function between<T>(a1: T, a2: T, a3: T) {
  return a2 <= a1 && a1 <= a3;
}

Good:

function between<T>(value: T, left: T, right: T) {
  return left <= value && value <= right;
}

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Use pronounceable variable names

If you can’t pronounce it, you can’t discuss it without sounding like an idiot.

Bad:

class DtaRcrd102 {
  private genymdhms: Date;
  private modymdhms: Date;
  private pszqint = '102';
}

Good:

class Customer {
  private generationTimestamp: Date;
  private modificationTimestamp: Date;
  private recordId = '102';
}

Use the same vocabulary for the same type of variable

Bad:

function getUserInfo(): User;
function getUserDetails(): User;
function getUserData(): User;

Good:

function getUser(): User;

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Use searchable names

We will read more code than we will ever write. It's important that the code we do write is readable and searchable. By not naming variables that end up being meaningful for understanding our program, we hurt our readers. Make your names searchable. Tools like TSLint can help identify unnamed constants.

Bad:

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

Good:

// Declare them as capitalized named constants.
const MILLISECONDS_IN_A_DAY = 24 * 60 * 60 * 1000;

setTimeout(restart, MILLISECONDS_IN_A_DAY);

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Use explanatory variables

Bad:

declare const users:Map<string, User>;

for (const keyValue of users) {
  // iterate through users map
}

Good:

declare const users:Map<string, User>;

for (const [id, user] of users) {
  // iterate through users map
}

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Avoid Mental Mapping

Explicit is better than implicit.
Clarity is king.

Bad:

const u = getUser();
const s = getSubscription();
const t = charge(u, s);

Good:

const user = getUser();
const subscription = getSubscription();
const transaction = charge(user, subscription);

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Don't add unneeded context

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

Bad:

class Car {
  carMake: string;
  carModel: string;
  carColor: string;

  name(): string{
    return `${this.carMake} ${this.carModel} (${this.carColor})`;
  }
}

Good:

class Car {
  make: string;
  model: string;
  color: string;

  name(): string{
    return `${this.make} ${this.model} (${this.color})`;
  }
}

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Use default arguments instead of short circuiting or conditionals

Default arguments are often cleaner than short circuiting.

Bad:

function loadPages(count: number) {
  const loadCount = count || 10;
}

Good:

function loadPages(count: number = 10) {
}

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Comments

The use of a comments is an indication of failure to express without them. Code should be the only source of truth.

Don’t comment bad code—rewrite it.
— Brian W. Kernighan and P. J. Plaugher

Prefer self explanatory code instead of comments

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

Bad:

// Check if subscription is active.
if (subscription.endDate < Date.now) {  }

Good:

const isSubscriptionActive = subscription.endDate < Date.now;
if (isSubscriptionActive) { /* ... */ }

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Don't leave commented out code in your codebase

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

Bad:

class User {
  name: string;
  email: string;
  // age: number;
  // jobPosition: string;
}

Good:

class User {
  name: string;
  email: string;
}

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: Added type-checking (LI)
 * 2015-03-14: Implemented combine (JR)
 */
function combine(a:number, b:number): number {
  return a + b;
}

Good:

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

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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.
Optionally you can use IDE support for code folding (see Visual Studio Code folding regions).

Bad:

////////////////////////////////////////////////////////////////////////////////
// Client class
////////////////////////////////////////////////////////////////////////////////
class Client {
  id: number;
  name: string;
  address: Address;
  contact: Contact;

  ////////////////////////////////////////////////////////////////////////////////
  // public methods
  ////////////////////////////////////////////////////////////////////////////////
  public describe(): string {
    // ...
  }

  ////////////////////////////////////////////////////////////////////////////////
  // private methods
  ////////////////////////////////////////////////////////////////////////////////
  private describeAddress(): string {
    // ...
  }

  private describeContact(): string {
    // ...
  }
};

Good:

class Client {
  id: number;
  name: string;
  address: Address;
  contact: Contact;

  public describe(): string {
    // ...
  }

  private describeAddress(): string {
    // ...
  }

  private describeContact(): string {
    // ...
  }
};

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