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JavaScript JavaScript Loops, Arrays and Objects Tracking Multiple Items with Arrays Two-Dimensional Arrays

Marc Murray
Marc Murray
4,618 Points

Couple of quirks I'm noticing with arrays, they seem to be acting strangely for me.

Just a couple of oddities I have noticed that seem to contradict what the course has shown me so far, just wondering if anyone could clear up the confusion I am having at the moment?

  1. When I use a loop to access items in an array, it seems to always count one further than it should and prints the value 'undefined" for the last item every time. I can fix this using things like (playlist.length - 1); in my loops but it doesn't seem like I should need to.

  2. This function here so far prints both the song title and artist name, which is meant to be the eventual goal of this video, then when I add [0] after [i] like instructed, the console then warns me that songs[i] is undefined. My code is below. NOTE: Figured out the second one, my mistake!

There's probably something ridiculous I am overlooking but the first question in particular has been niggling at me since the beginning of the section on arrays. Thanks to anyone who'll take a look! :)

var playlist = [
['I Did It My Way',' Frank Sinatra'],
['Orangutan Blues', ' Mick Delamere'],
['Strongmen Defenders', ' The Country Clubs Wastrels'],
['Wheres My Weed At', ' Cooncoon']

function printSongs(songs) {
    var listHTML = '<ol>';
    for ( var i = 0; i <= songs.length; i += 1) {
        listHTML += '<li>' + songs[i][0] + ' by ' + songs[i][1] + ' </li>';
listHTML += '</ol>';


1 Answer

LaVaughn Haynes
LaVaughn Haynes
12,397 Points

remove the "=" in your loop

//for ( var i = 0; i <= songs.length; i += 1) {
for ( var i = 0; i < songs.length; i += 1) {

Remember arrays start counting from 0, not 1. Since you are starting with 0 you want to stop before i equals the length of your array. For example, you have for elements so your loop is good for "i is equal to 0, 1, 2, and 3". i equals 4 (the length of your array) is undefined.

Marc Murray
Marc Murray
4,618 Points

Derp, I had this concept yesterday and had since totally forgotten it. Thanks!