export const isUserSignedIn = (userId:string, username?: string): boolean => { if(userId = "abc"){ console.log("singin", username); return true; } else { console.log("not singin"); return false; } } export const isUserSignedIn02 = (userId:string, username: string = "no name") => { if(userId = "abc"){ console.log("singin", username); return true; } else { console.log("not singin"); return false; } } export const sumProductsPrice = (...productsPrice/*いくつでもok*/: number[]): number => { return productsPrice.reduce((prevTotal/*一つ一つ取り出した一つ前の計算値*/: number, productsPrice: number) => { return prevTotal + productsPrice }, 0/*prevTotalの初期値*/) } type message = (message: string) => void
import {isUserSignedIn, isUserSignedIn02} from "./function/parameters" isUserSignedIn("abc", "@rise"); isUserSignedIn02("abc"); const sum = sumProductsPrice(1, 2, 3, 4, 5); console.log(sum);