Exercises: JavaScript Objects

Standard Exercises

0. What does the following code do? What do you think it prints out? Try it out and see.

var person = {
    firstName: "John",
    lastName: "Wordsworth"
};

console.log(person.firstName);
console.log(person["lastName"]);

1. What does the following code do? What do you expect it to print out?

var contact = {};
contact["fullName"] = "John Wordsworth";
contact["mobile"] = "01234567890";

console.log(contact.fullName + " " + contact.mobile);

2. You can access an object's properties using either a dot followed by the name of the property object.property or by using square brackets containing a string with the property name object["property"]. Like with an array, you can read or write to properties this way. Conver the following code to use the square brackets format for accessing object properties;

var tweet = {
    username: "@JohnWordsworth",
    message: "Hello Everyone!",
    likes: 6
}

console.log( tweet.username );          // Should print "@JohnWordsworth"
console.log( tweet.message );           // Should print "Hello Everyone!"

3. Similarly, convert the following code to use the dot format instead of square brackets.

var tweet = {
    username: "@JohnWordsworth",
    message: "Goodbye Everyone!",
    likes: 0
}

console.log( tweet["username"] + " tweeted " + tweet["message"] );

4. Create a variable called song as an object to represent a song in a music player. The song object should have the properties "title" and "artist". Use the following code to ensure you have created your object correctly;

// Define your song object here

console.log( song.title );          
console.log( song.artist );

5. Write the function printContactName(contact); that takes an object and prints out the 'name' property of that object if it is not null. Test your function with the following code;

var contact1 = {
    name: "John Wordsworth",
    address: "1 Infinite Loop"
};

var contact2 = {
    address: "2 Infinite Loop",  
};

printContactName(contact1);         // Should print "John Wordsworth"
printContactName(contact2);         // Should not print anything (as it has no name)

Advanced Exercises

6. Now it's time to create an array containing objects. Create a variable called playlist which is an array containing 3 song objects. Each song object should have a 'title' and 'artist' property. Use 3 songs that you love!

// Declare variable 'playlist'

console.log(playlist.length);       // Should print '3'
console.log(playlist[0].title);     // Should print the title of your first song
console.log(playlist[2].artist);    // Should print the title of your third song

7. Use a for loop to print the title of every object in your playlist on a separate line.

8. Turn your previous answer into a function called printPlaylist(playlist); which will print the title of every song in a playlist.