clean-code-ngx

Table of Contents

1. Introduction
2. Variables
3. Functions
4. Objects and Data Structures
5. Classes

Introduction

angular-cli is written in typescript and in latest javascript. Angualr has official style guide to Angular syntax, conventions, and application structure. Which is adapted for clean code ngx. This repo is not a offical guidlines but a concept for how we write good code.

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 years of collective experience by developers.

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 Typescript/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!

Inspired from clean-code-javascript and clean-code-php. Thanks to Mr. Ryan McDermott and Mr. Piotr Plenik.

Variables

Use meaningful and pronounceable variable names with data type

Global Variables

If you defined variable as global variable provide control access keyword with variable data type Bad:

userid: any;

Good:

public id: number;
protected password: string;
public primes: number[] = [10, 2, 3]; 

variables with scope

If variable has scope with function only then define it as local variable Bad:

carid: number;

let getCar = (car) => {
  this.carid = car.id;
  // ....
}

Good:

let getCar = (car) => {
  const id = car.id;
  // ....
}

Use identical comparison

Identical comparision has more efficent then simple comparison. Identical comparison will compare type and value
Bad:

const x = '10';
const y = 10;

if( x == y ) {
  //The expression will always passes
}

Apparently both variable has same value but different type so in simple comparison it will return true and sometimes it leads to unexpected results

Good:

if( x === y ) {
    //The expression isn't verified
}

Use the same vocabulary for the same type of variable

Bad:

let getClientInfo = () => {};
let getClientData = () => {};
let getClientRecord = () => {};

Good:

let getClient = () => {};

Use searchable names

We will read more code than we will ever write. It is 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 ESLint can help identify unnamed constants.

Bad:

// What the heck is 1 for?
if (user.access && 4) {
  ...
}

Good:

class User {
  public ACCESS: object = {
    READ: 1,
    CREATE: 2,
    UPDATE: 4,
    DELETE: 8
  };
}

if (user.access && this.ACCESS.UPDATE) {
    ...
}

Don't add unneeded context

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

Bad:

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

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

Good:

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

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

Use default arguments instead of short circuiting or conditionals

Default arguments are often cleaner than short circuiting. Be aware that if you use them, your function will only provide default values for undefined arguments. Other "falsy" values such as '', "", false, null, 0, and NaN, will not be replaced by a default value.

Bad:

let countryCode = (code) => {
  const code = code || '+01';
  ...
}

Good:

let countryCode = (code = '+01') => {
  ...
}

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Functions

Function arguments type and return type

you have to passed argument type and return type to function where its necessary

let sumAmount = function(x: number, y: number): number { return x + y; };

Function arguments (2 or fewer ideally)

Number of argument parameters is apparently gives you convenient way to interact data or makes testing with function easily. Having more than three leads to a combinatorial explosion where you have to test tons of different cases with each separate argument.

One or two arguments is the ideal case, and three should be avoided if possible. Anything more than that should be consolidated. Usually, if you have more than two arguments then your function is trying to do too much. In cases where it's not, most of the time a higher-level object will suffice as an argument.

Since Typescript allows you to make objects on the fly, without a lot of class boilerplate, you can use an object if you are finding yourself needing a lot of arguments.

To make it obvious what properties the function expects, you can use the ES2015/ES6 destructuring syntax. This has a few advantages:

1. When someone looks at the function signature, it's immediately clear what properties are being used.
2. Destructuring also clones the specified primitive values of the argument object passed into the function. This can help prevent side effects. Note: objects and arrays that are destructured from the argument object are NOT cloned.
3. Linters can warn you about unused properties, which would be impossible without destructuring.

Bad:

let showMenu = (title, body, buttonText, cancellable) => {
  ...
}

Good:

let showMenu = (options: object) => {
  ...
}

let options = {
  title: 'Foo',
  body: 'Bar',
  buttonText: 'Baz',
  cancellable: true
}

showMenu(options);

Functions should do one thing

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.

Bad:

let emailClients = (clients) => {
  clients.forEach((client) => {
    let record = database.lookup(client);
    if (record.isActive()) {
      email(client);
    }
  }
}

Good:

let emailActiveClients = (clients) => {
  clients
    .filter(isActiveClient)
    .forEach(email);
}

let isActiveClient = (client) => {
  let record = database.lookup(client);
  return record.isActive();
}

Function names should say what they do

Bad:

let fetchList = (parent) => {
  ...
}

// It's hard to tell from the function name what is fetched
this.fetchList('document');

Good:

let fetchFoldersList = (parent) => {
  ...
}

Avoid nesting too deeply and return early

Explicit is better than implicit.

Bad:

let isHoliday = (day) => {
  if (day) {
    if (typeof day === 'string') {
      day = day.toLowerCase();
      if (day === 'saturday') {
        return true;
      } else if (day === 'sunday') {
        return true;
      } else {
        return false;
      }
    } else {
      return false;
    }
  } else {
    return false;
  }
}

Good:

let isHoliday = (day: string): boolean => {
  if (!day) {
   return false; 
  }
  const holidays = ['saturday', 'sunday'];

  return (holidays.some(x => x === day.toLowerCase())) ? true : false;
}

Functions should only be one level of abstraction

When you have more than one level of abstraction. Make code to reusable and flexible.

Bad:

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

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

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

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

Good:

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

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

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

let parseBetterJSAlternative = (code) => {
  let tokens = this.tokenize(code);
  let ast = this.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.

Imagine if you run a restaurant and you keep track of your inventory: all your tomatoes, onions, garlic, spices, etc. If you have multiple lists that you keep this on, then all have to be updated when you serve a dish with tomatoes in them. If you only have one list, there's only one place to update!

Oftentimes you have duplicate code because you have two or more slightly different things, that share a lot in common, but their differences force you to have two or more separate functions that do much of the same things. Removing duplicate code means creating an abstraction that can handle this set of different things with just one function/module/class.

Getting the abstraction right is critical, that's why you should follow the SOLID principles laid out in the Classes section. Bad abstractions can be worse than duplicate code, so be careful! Having said this, if you can make a good abstraction, do it! Don't repeat yourself, otherwise you'll find yourself updating multiple places anytime you want to change one thing.

Bad:

let showDevelopersList = (developers) => {
  developers.forEach((developer) => {
    let salary = developer.calculateSalary();
    let experience = developer.getExperience();
    let projects = developer.getExecutedProjects();
    let data = {
      salary: salary,
      experience: experience,
      projects: projects
    };
    render(data);
  });
}

let showManagerList = (managers) => {
  managers.forEach((manager) => {
    let salary = manager.calculateSalary();
    let experience = manager.getExperience();
    let projects = developer.getManagedProjects();
    let data = {
      salary: salary,
      experience: experience,
      projects: projects
    };
    render(data);
  });
}

Good:

let showEmployeeList = (employees) => {
  employees.forEach((employee) => {
    let salary = employee.calculateSalary();
    let experience = employee.getExperience();
    let data = {
      salary: salary,
      experience: experience
    };

    switch (employee.type) {
      case 'manager':
        data.project = employee.getManagedProjects();
        break;
      case 'developer':
        data.project = employee.getExecutedProjects();
        break;
    }
    render(data);
  });
}

Set default objects with Object.assign

Bad:

let configurations = {
  host: null,
  user: null,
  password: null,
  dbname: 'database1'
};

let connection = (config: object) => {
  config.host = config.host || 'localhost';
  config.user = config.user || 'root';
  config.password = config.password || '123';
  config.dbname = config.dbname || 'defaultDB';
}

this.connection(configurations);

Good:

let configurations = {
  dbname: 'database_new'
};

let connection = (config: object) => {
  config = Object.assign({
    host: 'localhost',
    user: 'root',
    password: '123',
    dbname: 'defaultDB'
  }, config);

  // config now equals: {host: "localhost", user: "root", password: "123", dbname: "defaultDB"}
  // ...
}

this.connection(configurations);

Don't use flags as function parameters

Sometimes flags uses in function argument to perform different action based on flag. But function should do one thing. Spit funtions by thier different code paths based on flags

Bad:

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

Good:

let createFile = (name) => {
  fs.create(name);
}

let createTempFile = (name) => {
  createFile(`./temp/${name}`);
}

Avoid Side Effects (part 1)

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.

Now, you do need to have side effects in a program on occasion. Like the previous example, you might need to write to a file. What you want to do is to centralize where you are doing this. Don't have several functions and classes that write to a particular file. Have one service that does it. One and only one.

The main point is to avoid common pitfalls like sharing state between objects without any structure, using mutable data types that can be written to by anything, and not centralizing where your side effects occur. If you can do this, you will be happier than the vast majority of other programmers.

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';

let splitIntoFirstAndLastName = () => {
  name = name.split(' ');
}

splitIntoFirstAndLastName();

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

Good:

let splitIntoFirstAndLastName = (name) => {
  return name.split(' ');
}

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

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

Avoid Side Effects (part 2)

In TypeScript, primitives are passed by value and objects/arrays are passed by reference. In the case of objects and arrays, if your 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. Let's imagine a bad situation:

The user clicks the "Purchase", button which calls a purchase function that spawns a network request and sends the cart array to the server. Because of a bad network connection, the purchase function has to keep retrying the request. Now, what if in the meantime the user accidentally clicks "Add to Cart" button on an item they don't actually want before the network request begins? If that happens and the network request begins, then that purchase function will send the accidentally added item because it has a reference to a shopping cart array that the addItemToCart function modified by adding an unwanted item.

A great solution would be for the addItemToCart to always clone the cart, edit it, and return the clone. This ensures that no other functions that are holding onto a reference of the shopping cart will be affected by any changes.

Two caveats to mention to this approach:

1. There might be cases where you actually want to modify the input object, but when you adopt this programming practice you will find that those cases are pretty rare. Most things can be refactored to have no side effects!

2. Cloning big objects can be very expensive in terms of performance. Luckily, this isn't a big issue in practice because there are great libraries that allow this kind of programming approach to be fast and not as memory intensive as it would be for you to manually clone objects and arrays.

Bad:

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

Good:

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

Favor functional programming over imperative programming

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

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
  .map(output => output.linesOfCode)
  .reduce((totalLines, lines) => totalLines + lines);

Encapsulate conditionals

Bad:

if (user.access === 'edit' && this.authenticate(key, user.hash)) {
  ...
}

Good:

let accessMenu = (user, key) => {
  return user.access === 'edit' && this.authenticate(key, user.hash);
}

if (this.accessMenu()) {
  ...
}

Avoid negative conditionals

Bad:

let isDOMNodeNotPresent = (node) => {
  // ...
}

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

Good:

let isDOMNodePresent = (node) => {
  // ...
}

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

Avoid duplication, Make common

Bad:

export class Missile {
  // ...
  let getMaxAltitude () => {}
  let getAltitude = () => {
    return this.getMaxAltitude();
  }
}

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

Make one common service and placed all reusable and common function into that service Good:

// common.service.ts
@Injectable()
export class Common {
  // ...
  let getMaxAltitude = () => {}
}

export class Airplane {
  constructor(private common: Common) {}
  // ...
  getCruisingAltitude() {
    return this.common.getMaxAltitude() - this.getPassengerCount();
  }
}

export class Missile {
  constructor(private common: Common) {}
  // ...
  getCruisingAltitude() {
    return this.common.getMaxAltitude()
  }
}

Avoid type-checking (part 1)

TypeScript 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.

Bad:

let 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:

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

Avoid type-checking, pass type in arguments (part 2)

If you are working with basic primitive values like strings and integers, and you can't use polymorphism but you still feel the need to type-check, you should consider using TypeScript. We can add types to each of the parameters and then to the function itself to add a return type.

Bad:

let combine = (val1, val2) => {
  if (typeof val1 === 'string' && typeof val2 === 'string') {
    return val1 + val2;
  }

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

Good:

let combine = (val1: string, val2: string): string => { return val1 + val2; };

Remove dead code & unwanted debug script

Dead code and debug 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.

Bad:

let oldRequestModule = (url) => {
  // ...
}

let newRequestModule = (url) => {
  console.log('URL', url);
  // ...
}

const req = newRequestModule;
debugger;
let inventoryTracker = ('apples', req, 'www.inventory-awesome.io') => {};

Good:

let newRequestModule = (url) => {
  // ...
}

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

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Objects and Data Structures

Use getters and setters

Using getters and setters to access data on objects could be 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.
• You can lazy load your object's properties, let's say getting it from a server.

Bad:

class Bank {
  let makeBankAccount = () => {
    // ...
    return {
      balance: 0,
    };
  }
}

let bank = new Bank();
const account = bank.makeBankAccount();
account.balance = 100;

Good:

class Bank {
  private _account: object;

  get balance(): object {
      return this._account;
  }

  set balance(amount: number) {
    this._account.balance = amount;
  }
}

let bank = new Bank();
const account = bank.makeBankAccount();
account.balance(100);

Make objects have private members

This can be accomplished through closures (for ES5 and below).

Bad:

let Employee = (name: string) => {
  this.name = name;
};

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

let 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:

let makeEmployee = (name) => {
  return {
    getName() {
      return name;
    },
  };
}

let employee = this.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

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Classes

Use method chaining

This pattern is very useful in TypeScript 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.

Bad:

class Car {
  public color: string;
  
  let setColor = (color) => {
    this.color = color;
  }

  let save = () => {
    console.log(this.color);
  }
}

const car = new Car();
car.setColor('pink');
car.save();

Good:

const car = this.car.setColor('pink').save();

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