what does array.concat() do in javascript code example

Example 1: javascript concat two arrays

//ES6
const array3 = [...array1, ...array2];

Example 2: concat array javascript

const letters = ['a', 'b', 'c'];
const numbers = [1, 2, 3];

const newArray = letters.concat(numbers);
// newArrat is ['a', 'b', 'c', 1, 2, 3]