はじめに

Typescriptではいろいろな関数の書き方があるので簡単にまとめてみました。

戻り値の整理

src/function/basic.ts

export const logMessage = (message: string): void => {
  console.log('sample 1:', message)
}

src/index.ts

import { logMessage } from './function/basic'
logMessage('Hello TypeScript!')
//sample 1: Hello TypeScript!

src/function/basic.ts

export function logMessage2(message: string): void {
  console.log('sample 2:', message)
}

src/index.ts

import { logMessage2 } from './function/basic'
logMessage2('Hello TypeScript!')
//sample 2: Hello TypeScript!

src/function/basic.ts

export const logMessage3 = function (message: string): void {
  console.log('sample 3:', message)
}

src/index.ts

import { logMessage3 } from './function/basic'
logMessage3('Hello TypeScript!')
//sample 3: Hello TypeScript!

src/function/basic.ts

export const logMessage4 = (message: string): void => console.log('sample 4:', message)

src/index.ts

import { logMessage4 } from './function/basic'
logMessage4('Hello TypeScript!')
//sample 4: Hello TypeScript!

src/function/basic.ts

export const alwaysThrowError = (message: string): never => {
  throw new Error(message)
}