Signal#Signal

Signals are what Phaser uses to handle events and event dispatching.
You can listen for a Signal by binding a callback / function to it.
This is done by using either Signal.add or Signal.addOnce.

For example you can listen for a touch or click event from the Input Manager
by using its onDown Signal:

game.input.onDown.add(function() { ... });

Rather than inline your function, you can pass a reference:

game.input.onDown.add(clicked, this);
function clicked () { ... }

In this case the second argument (this) is the context in which your function should be called.

Now every time the InputManager dispatches the onDown signal (or event), your function
will be called.

Very often a Signal will send arguments to your function.
This is specific to the Signal itself.
If you're unsure then check the documentation, or failing that simply do:

Signal.add(function() { console.log(arguments); })

and it will log all of the arguments your function received from the Signal.

Sprites have lots of default signals you can listen to in their Events class, such as:

sprite.events.onKilled

Which is called automatically whenever the Sprite is killed.
There are lots of other events, see the Events component for a list.

As well as listening to pre-defined Signals you can also create your own:

var mySignal = new Phaser.Signal();

This creates a new Signal. You can bind a callback to it:

mySignal.add(myCallback, this);

and then finally when ready you can dispatch the Signal:

mySignal.dispatch(your arguments);

And your callback will be invoked. See the dispatch method for more details.