merge two arrays using concat() or push.
/**
* Concat
*/
var mergeTo = [4,5,6],
mergeFrom = [7,8,9];
mergeTo = Array.prototype.concat(mergeTo, mergeFrom);
mergeTo; // is: [4, 5, 6, 7, 8, 9]
/**
* Push
*/
var mergeTo = [4,5,6],
mergeFrom = [7,8,9];
Array.prototype.push.apply(mergeTo, mergeFrom);
mergeTo; // is: [4, 5, 6, 7, 8, 9]
/**
* TODO: run performance test
*/