If you want to modify the original array instead of returning a new array, use .push()...
array1.push.apply(array1, array2);
array1.push.apply(array1, array3);
I used .apply to push the individual members of arrays 2 and 3 at once.
or...
array1.push.apply(array1, array2.concat(array3));
To deal with large arrays, you can do this in batches.
for (var n = 0, to_add = array2.concat(array3); n < to_add.length; n+=300) {
array1.push.apply(array1, to_add.slice(n, n+300));
}
If you do this a lot, create a method or function to handle it.
var push_apply = Function.apply.bind([].push);
var slice_call = Function.call.bind([].slice);
Object.defineProperty(Array.prototype, "pushArrayMembers", {
value: function() {
for (var i = 0; i < arguments.length; i++) {
var to_add = arguments[i];
for (var n = 0; n < to_add.length; n+=300) {
push_apply(this, slice_call(to_add, n, n+300));
}
}
}
});
and use it like this:
array1.pushArrayMembers(array2, array3);
var push_apply = Function.apply.bind([].push);_x000D_
var slice_call = Function.call.bind([].slice);_x000D_
_x000D_
Object.defineProperty(Array.prototype, "pushArrayMembers", {_x000D_
value: function() {_x000D_
for (var i = 0; i < arguments.length; i++) {_x000D_
var to_add = arguments[i];_x000D_
for (var n = 0; n < to_add.length; n+=300) {_x000D_
push_apply(this, slice_call(to_add, n, n+300));_x000D_
}_x000D_
}_x000D_
}_x000D_
});_x000D_
_x000D_
var array1 = ['a','b','c'];_x000D_
var array2 = ['d','e','f'];_x000D_
var array3 = ['g','h','i'];_x000D_
_x000D_
array1.pushArrayMembers(array2, array3);_x000D_
_x000D_
document.body.textContent = JSON.stringify(array1, null, 4);