Object Literal Delegates

Furthering on from my introduction tutorial to object literals in JavaScript, this is a slightly more advanced tutorial on how to set up delegates. A delegate is essentially a callback that one object can register for, usually receiving data from the object doing the delegating.

In this tutorial, you’ll learn how to:

  • Set up a method to add an infinite number of delegates
  • Set up a method to remove a delegate
  • Send messages to the delegates

Here’s a working example:

If the setup of the objects themselves is confusing then make sure you’ve read my introduction tutorial, but here’s a rundown of what I’ve done:

There are three objects here, the Map object and two other objects which will be a Map delegate. The Map object has a property called  delegates, which will hold an array of all the delegates you add. The Map object also has three methods: .addDelegate(), .removeDelegate() and .sendDataToDelegates(). These are all pretty self-explanatory.

The two delegate objects, MapDelegate and AnotherDelegate both have to implement  .coordinatesChanged() which is a required method because otherwise the script will break when Map tries to call it. You can make a method optional by first checking if it’s defined before calling it for each delegate.

As you can see, the delegate objects both implement the .coordinatesChanged() method, but they do different things with the data (one prints the coordinates to the console, the other alerts the user with a dialog). All they care about is that the coordinates have changed and what the new coordinates are, they do their own thing with the new data.

Object Literals; Something Every New JavaScript Dev Needs To Know

JavaScript is a funny thing, it’s extremely powerful in helping us make amazing and interactive websites (especially coupled with the fantastic jQuery library), but it’s really difficult to keep the code tidy and structured. Enter ‘Object Literals’.

Object literals are essentially a list of key:value pairs. Each key can hold anything as a value, even another object.

Here’s an example of passing another object literal as a value to the  born  key.

Note that the last key:value pair in an object doesn’t have a comma after, if you add a comma it will break the script in some browsers (namely IE).

So you’ve learned about the basics of an object literal, but you need to know how they’re actually useful. You can assign an object literal to a variable: Continue reading “Object Literals; Something Every New JavaScript Dev Needs To Know”