What is spread operator in ES6?

The spread operator is represented by three dots (…) to obtain the list of parameters. It allows the expansion of an iterable such as array or string in places where more than zero arguments are expected.
The spread operator syntax is similar to the rest operator, but functionality is entirely opposite to it. It is also used to combine or to perform the concatenation between arrays. Let’s understand it by an example.

let n1 = [40,50,60];
let n2 = [10,20,30,…n1,70,80,90,100];