function

default value

(function(x = 'foo') {
  console.log('Hello ' + x);
})();
//  Hello foo

rest

Using in function declaration parameters

Example:

function func(a, b, ...args) {
  console.log(args.length);
}
func(1, 2, 3, 4);  //  2

spread

Using in function(variable); Example:

function add(x, y) {
  return x + y;
}
let nums = [2, 3];
let result = add(...nums);
console.log(result);  //  5

Do more in array~

Can replace the apply in array;

arrayA.concat(arrayB) => arrayA = [...arrayA, ...arrayB];