obaranovskyi

/** @deprecated use User class instead */
class OldUser {}

class User {

  /** @deprecated */
  constructor(public username: string, public age: number) {}

  /** @deprecated */
  static createUser(username: string, age: number) { 

obaranovskyi

class User {
  username: string;
  age: number;

  constructor(username: string,age: number) {
    this.username = username;
    this.age = age;
  }

  static [propName: string]: string | number;

obaranovskyi

class User {
  username: string;
  age: number;

  constructor(username: string,age: number) {
    this.username = username;
    this.age = age;
  }

  [propName: string]: string | number;

obaranovskyi

function userCount() { 
  /* Mock data */
  return 15;
};

class User {
  id = 0;
  static count: number = 0;

  constructor(

obaranovskyi

{
  "compilerOptions": {
    "noImplicitOverride": true
  }
}

obaranovskyi

class Employee {
  doWork() {
    console.log('I\'m working!');
  }
}

class Developer extends Employee {
  override doWork() {
    console.log('I\'m programming!')
  }

obaranovskyi

const roles = ['read', 'write', 'readAndWrite'] as const;

type Roles = typeof roles[number]; 
// equals to this
// type Roles = "read" | "write" | "readAndWrite"

// or even like this
type RolesInCapital = Capitalize<typeof roles[number]>;
// equals to this
// type RolesInCapital = "Read" | "Write" | "ReadAndWrite"

obaranovskyi

const email = 'john@gmail.com'; // type 'john@gmail.com'
const phones = [8494922901, 1238399293]; // type number[]
const session = { id: 123, name: 'x1keck323jKJdf1' };
// type 
// {
//     id: number;
//     name: string;
// }

const username = 'John' as const; // type 'John'

obaranovskyi

function valueCheck(value: string | number) {
  if (typeof value === "string") {
    // value has type string
  } else if (typeof value === "number") {
    // value has type number
  } else {
    value; // value has type never
  }
}

obaranovskyi

function endlessWhile(): never {
  while(true) {
    /* ... */
  }
}