Javascript Array Concat not working. Why?

The concat method doesn't change the original array, you need to reassign it.

if ( ref instanceof Array )
   this.refs = this.refs.concat( ref );
else
   this.refs.push( ref );

Here is the reason why:

Definition and Usage

The concat() method is used to join two or more arrays.

This method does not change the existing arrays, but returns a new array, containing the values of the joined arrays.

You need to assign the result of the concatenation back in the array that you have.

To expand on Konstantin Dinev:

.concat() doesn't add to current object, so this will not work:

foo.bar.concat(otherArray);

This will:

foo.bar = foo.bar.concat(otherArray);