Eloquent Javascript: Exercise: A list

Question

I am learning JavaScript from a book called 'Eloquent Javascript'

I'm trying to solve the exercise described here: http://eloquentjavascript.net/04_data.html#h_nSTX34CM1M

I managed to work out that this code works:

function arrayToList(array) {

  var list = null;

  for (var i = array.length - 1; i >= 0; i--)
    list = {
      value: array[i],
      rest: list
    };
  return list;
}

console.log(arrayToList([1, 2, 3]));

Result: { value: 1, rest: { value: 2, rest: { value: 3, rest: null } } }

So far, so good, and according to the book this is the right solution. BUT!

When I try to run the same thing but instead with a longer array, let's say:

console.log(arrayToList([1, 2, 3, 4, 5]));

The result is: { value: 1, rest: { value: 2, rest: { value: 3, rest: [Object] } } }

Why is this? Is my code wrong?

Answer 1

There's nothing wrong with a longer array. console.log() is a non-standard, browser-specific implementation and some implementations set a cap on how many levels of object nesting they will display. When they hit that level, they just display [Object] rather than recurse into it to show deeper nesting.

If you actually set a breakpoint and examine your variable in the debugger, you will see you can expand the nested levels as deep as it goes and see everything.

Or, you could do this:

console.log(JSON.stringify(arrayToList([1, 2, 3, 4, 5])));

to manually convert the whole thing to a string before using console.log() on it.