Concat in an empty array in Javascript

Question

I was browsing through some code and I was wondering how this could be useful

grid.push([].concat(row));

In my understanding it is the same as<

Answer 1

With grid.push([row]); you are pushing an array containing the row itself. If row is an array (e.g. [0, 1, 2]). You will push an array containing another array (i.e. [[0, 1, 2]]).

With grid.push([].concat(row));, you are pushing an array containing the elements contained in row (i.e. [0, 1, 2]).

However it is unclear why it is not just written grid.push(row) which, if row is an array, could seem more or less the same as grid.push([].concat(row));.

I can find two explanations for this:

1. row is not an array but an "array-like" object and [].concat(row) is used to convert it (just like Array.from could do).

2. Your coder does not want to push row but a copy of row instead that protected against any further modification of the original row.