Spread

An array or object can be quickly copied into another array or object by using the Spread Operator (...). It allows an iterable such as an array to be expanded in places where zero or more arguments (for function calls) or elements (for array literals) are expected, or an object expression to be expanded in places where zero or more key-value pairs (for object literals) are expected.

Here are some examples of it:

let arr = [1, 2, 3, 4, 5]; 

console.log(...arr); 
// Result: 1 2 3 4 5

let arr1;
arr1 = [...arr]; //copies the arr into arr1 

console.log(arr1);    //Result: [1, 2, 3, 4, 5]

arr1 = [6,7];
arr = [...arr,...arr1];

console.log(arr);   //Result: [1, 2, 3, 4, 5, 6, 7]