concat.js

var array1 = [1, 2, 3, 4];
var array2 = [5, 6, 7, 8];
var array3 = [9, 10, 11, 12];

var array = array1.concat(array2, array3);

console.log(array);
// [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]