Concatenate Arrays with concat - Why newArray = oldArray

Fairly straightforward lesson regarding the concat function to add one array onto the end of another. My question is in regard to the line

newArray = oldArray;

What is the purpose of this and why when I remove it or place it below .concat function does it return the array [1,2,3]?

Thanks for any input.

var oldArray = [1,2,3];
var newArray = [];

var concatMe = [4,5,6];

// Only change code below this line.
newArray = oldArray;

newArray = oldArray.concat(concatMe);

oldArray references [1, 2, 3], so if you remove the following line:

newArray = oldArray;

you are left with the following code:

newArray = oldArray.concat(concatMe);

The above code concatenates concatMe which references [4, 5, 6] to the end of oldArray

It is just the starting code. The challenge expects you to either delete or not. It does not change the outcome. If you leave it in or delete the above line, newArray still becomes [ 1, 2, 3, 4, 5, 6 ]

If you instead place the same line (newArray = oldArray;) below the last line ( newArray = oldArray.concat(concatMe);), then newArray will be [1, 2, 3].