Convert an array to a list of nested objects - Eloquent Javascript 4.3

Question

I am looking at this exercise from the book Eloquent Javascript, Chapter 4 - A List for quite some time and I\'m trying to understand how this particular function works:

Answer 1

TL;DR: In each iteration, we create a new object containing the object from last iteration.

In the line list = {value: array[i], rest: list};, the statement on the right of the = gets evaluated first. This means we create an object {value: array[i], rest: list}, containing the current values of array[i] and list. In the first iteration, list is null and array[i] is 20, so the object looks like this:

{value: 20, rest: null}

Only then do we assign this object to list.

In the next iteration, list isn’t null anymore, but {value: 20, rest: null}. So now, the object we create and assign to list looks like this:

{value: 10, rest: {value: 20, rest: null}}