【TypeScript】プリミティブ型

目次

• number
• string
• boolean
• void
• null
• undefined
• any

number

let year: number = 2000
// year = false
// error TS2322: Type 'boolean' is not assignable to type 'number'.
console.log(year)

let age: number = 0x2b

string

let name: string = "田中"
// name = 10
// error TS2322: Type 'number' is not assignable to type 'string'.
console.log(name)

boolean

let isFinished: boolean = true
isFinished = false
// isFinished = 1 
// error TS2322: Type 'number' is not assignable to type 'boolean'.
console.log({ isFinished })

void

// いかなる返り値も持たないことを明示
function returnNothing(): void {
  console.log("don't return anything")
}

console.log(returnNothing())

null

// nullのみ
let absence: null = null
// absence = "moji"
// error TS2322: Type '"moji"' is not assignable to type 'null'.

undefined

// undefinedのみ
let data: undefined = undefined
// data = 329
// error TS2322: Type '329' is not assignable to type 'undefined'.

any

// いかなる値もエラーはなし
let year: any = 2000
// year = false
// エラーなし
console.log(year)