Rest parameter

The rest parameter is used to represent an indefinite number of arguments as an array. The important point here is only the function's last parameter can be a "rest parameter". This feature has been introduced to reduce the boilerplate code that was induced by the arguments.

function sum(...args) {
return args.reduce((previous, current) => {
return previous + current;
});
}

console.log(sum(1, 2, 3)); // 6
console.log(sum(1, 2, 3, 4)); // 10
console.log(sum(1, 2, 3, 4, 5)); // 15