Refactor Global Variables Out of Functions - Confusion on returning array

Tell us what’s happening:

I might have missed this earlier, below are two examples; 1st one passes the challenge, the second one doesn’t. I seem to recall that something similar in ruby will work- is this just a JS related rule?

Your code so far

// the global variable
var bookList = ["The Hound of the Baskervilles", "On The Electrodynamics of Moving Bodies", "Philosophiæ Naturalis Principia Mathematica", "Disquisitiones Arithmeticae"];

/* This function should add a book to the list and return the list */
// New parameters should come before the bookName one

// works!
function add (arr,bookName) {
    var newArr = [...arr]
    return newArr;

// does not work!
function add (arr,bookName) {
    var newArr = [...arr]
    return (newArr.push(bookName));
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**Link to the challenge:**

The second function doesn’t work because push() does not return the array on which it was called. Rather, it returns its new length.