Result order of Javascript concat method

Question

Is the order of the concatenation result always preserved?

var alpha = ['a', 'b', 'c'];
var numeric = [1, 2, 3];

alpha.concat(numeric);
// result in ['a', 'b', 'c', 1, 2, 3]

Answer 1

Yes, it is.

From MDN (emphasis mine):

The concat method creates a new array consisting of the elements in the object on which it is called, followed in order by, for each argument, the elements of that argument

From the ECMAScript spec (emphasis mine):

When the concat method is called with zero or more arguments, it returns an array containing the array elements of the object followed by the array elements of each argument in order.