JavaScript version
sum.js
const sum = (...args) => args.reduce((a, b) => a + b);TypeScript version
sum.ts
const sum = (...args: number[]): number => args.reduce((a, b) => a + b);Examples
examples.js
sum(1, 2, 3, 4); // 10const sum = (...args) => args.reduce((a, b) => a + b);const sum = (...args: number[]): number => args.reduce((a, b) => a + b);sum(1, 2, 3, 4); // 10