Rest and Spread Operators in ES6

ES6 added two important new operators: Rest and Spread. Technically they look the same ( ... => three dots) but they are used in different places.

Rest:

function sumUp(start, ...toAdd) {}

Transforms a list of arguments (1, 2, 3) into an array ([1, 2, 3]) which may be used inside the function. This behavior is triggered when used inside of a function argument list.

Spread:

let ids = [1, 2, 3, 4, 5, 6];
console.log(Math.max(...ids)); // prints 6

Transforms an array into a list of arguments. This behavior is triggered when used outside of a function argument list.