Primitive Types

• boolean.
• number.
• string.
• array.
• tuple:
  • Fixed number of elements whose types are known.
  • Variable length array types aren’t assignable to tuple types.
• enum.
• null.
• undefined.
• void.
• any.
• unknown: 任何类型都能分配给 unknown, 但 unknown 不能分配给其他基本类型.
• never:
  • switch default case guard (exhaustiveness check).
  • Reduce never intersection type.
  • Ignored in union type:
    • mapped conditional type.
    • distributive conditional type.

let num: number
let str: string
let bool: boolean
let boolArray: boolean[]
let tuple: [string, number]
let power: any

// 赋值任意类型
power = '123'
power = 123

// 它也兼容任何类型
power = num
num = power

function log(message: string): void {
  console.log(message)
}

function unknownColor(x: never): never {
  throw new Error('unknown color')
}

type Color = 'red' | 'green' | 'blue'

function getColorName(c: Color): string {
  switch (c) {
    case 'red':
      return 'is red'
    case 'green':
      return 'is green'
    default:
      return unknownColor(c)
  }
}