Typescript #

A programming language to built top of javascript, to address shortcomings of javascript. You can also say typescript is javascript with type checking.

Why do we need it? #

Benefits #

• Static typing 静态检查
• Code completion 代码编译
• Refactoring
• Shorthand Notation

Drawbacks #

• Compilation(编译)
  • .ts->compiler->.js
  • this process is called transpilation(转译)
  • browser don't understand typescript code, it need typescript compiler to compile and translate into javascript.
• Discipline(严格) in coding

Primitive Types #

javascript

• number
• string
• boolean
• null
• undefined
• object

typescript extension

• any can represent any kind of values
• unknown
• never values that never occur
• enum
• tuple a fixed length array where each element has a particular type

Advanced Types #

• type alias 类型别名 type
• type assertion 类型断言 as
• union types 联合类型 a | b
• optional chaining ?.
• nullish coalescing operator a ?? 10 (null, undefined)
• literal type 字面量类型 50

Object-Oriented Programming #

Access Modifiers #

• public
• private
• protect

class Account {
  readonly id: number
  owner: string
  private _balance: number
  nikename?: string

  constructor(
    id: number,
    owner: string,
    _balance: number,
  ) {
    this.id = id
    this.owner = owner
    this._balance = _balance
  }
}

// equals

class Account {
  nikename?: string

  constructor(
    public readonly id: number,
    public owner: string,
    private _balance: number,
  ) {}

  deposit(amount: number): void {
    if (amount <= 0)
      throw new Error('Invalid amount')
    this._balance += amount
  }

  get balance(): number {
    return this._balance
  }

  set balance(val: number) {
    if (val < 0)
      throw new Error('Invalid value')
    this._balance = val
  }
}

Index signature property #

class SeatAssignment {
  [seatNumber: string]: string;
}

const seats = new SeatAssignment()
seats.A1 = 'Dylan'
seats.A2 = 'Daniel'