Array concat method in JavaScript

Array concat is a method and an array property for concating one array onto another to archive merging of array elements.

Syntax for array concat;

const arr = [0,1,2,3]
const arrr = [4,5]
arr.concat(arrr)

// [0,1,2,3,4,5]

Merging nested arrays using spread operator.

It's possible to merge nested arrays to form a uniform array.

Take for instance you have two 2-dimensional arrays,
Or let's call them matrices

const arr2d = [[1,0],[0,1]]
//[[1,0],
// [0,1]]

const arrr2d = [[1,1],[0,1]]
//[[1,1],
// [0,1]]

For instance you want to reduce the two 2-dimentional arrays and create a new array instance;

[].concat(...arr2d.concat(...arrr2d))

// [1, 0, 0, 1, 1, 1, 0, 1]