rest arguments javascript

// es6 rest parameter 
function fun(...input){ 
    let sum = 0; 
    for(let i of input){ 
        sum+=i; 
    } 
    return sum; 
} 
console.log(fun(1,2)); //3 
console.log(fun(1,2,3)); //6 
console.log(fun(1,2,3,4,5)); //15                  

function sum(...numbers) {
	return numbers.reduce((accumulator, current) => {
		return accumulator += current;
	});
};
 
sum(1,2) // 3
sum(1,2,3,4,5) // 15