Objects

What you will learn

• Create basic objects
• Get/set object fields
• Run object methods

Now let’s put together everything we have learned so far.

• Objects are code entities with state and behavior.
  • The state is represented by variables which make up various properties or attributes.
  • The behavior is managed by functions the object can run; typically, these functions modify the state in some way.

JavaScript is not a true object-oriented language so these objects act more like key-value structures such as maps or dictionaries in other languages than like true objects.

When we use JavaScript objects, we create the blueprint and fill in the values at the same time.

• Each value needs a key which acts similar to a variable name. Even functions are mapped onto keys.

  For example, let’s say I wanted to create a gameCharacter which had a name, pos, and health and could change its pos with a move function:

var gameCharacter = {
  name: “Nimish”,
  pos: 2,
  health: 100,
  move: function(byAmount) {
    this.pos += byAmount;
  }
}

We’re doing quite a bit here so let’s start at the top.

1. We create a variable called GameCharacter that, instead of containing a single value or a list of values, contains some key-value pairs. You can see for the first three key-values the keys are the names of variables and the values are whatever values we want the gameCharacter to have at that time.
2. The move function is mapped to the move key and we will show you how to use that in a minute.
3. The last thing I want to point out here is the use of the “this” keyword. This just signifies we are changing the pos value which belongs to the currently working object.

With JavaScript objects, we can use them right at the time of declaration. If we wanted to get the attributes of gameCharacter, we use dot syntax like this:

var name = gameCharacter.name;
var pos = gameCharacter.pos;
var health = gameCharacter.health;

Similarly we can change those values like this:

gameCharacter.pos = 10;

Or by calling the move function (although this only changes pos):

Or by calling the move function (although this only changes pos):

This calls whatever is stored at the move key (in this case a function which needs one value passed into it).

• So although JavaScript objects are not true objects such as you might see in object-oriented languages like Java, they serve a similar purpose as data structures which contain multiple values to make up their state and functions which allow them to execute behaviors.

Try to add more values and functions to this object and then try creating your own custom objects.

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