on

function

Add event handlers to a map.

`map.on(eventType, handler)`

Listens to eventType on map and calls handler when the event is dispatched. This is simply a reference to can-event.on as all of can-event methods are available on DefineMap.

var map = new DefineMap({name: "Justin"})
map.on("name", function(ev, newVal, oldVal){
    newVal //-> "Brian"
    oldVal //-> "Justin"
});
map.name = "Brian";

Parameters

eventType {String}:
The type of event to bind this handler to.
handler {function(event, args...)}:
The handler to be called when this type of event fires The signature of the handler depends on the type of event being bound. See below for details.

Returns

{can-define/map/map}:

This map, for chaining.

Use

on binds event handlers to property changes on DefineMaps. When you change a property value, a property name event is fired, allowing other parts of your application to map the changes to the object.

This event is useful for noticing changes to a specific property.

var o = new DefineMap({name: "Justin"});
o.on('name', function(ev, newVal, oldVal) {
    console.log('The value of a changed.');
});

The parameters of the event handler for the property name event are:

ev The event object.
newVal The value of the property after the change. `
oldVal The value of the property before the change.

Here is a concrete tour through the property name event handler's arguments:

var o = new DefineMap({a: undefined, b: undefined});
o.on('a', function(ev, newVal, oldVal) {
    console.log(newVal + ', ' + oldVal);
});

o.a = 'Alexis';       // Alexis, undefined
o.set('a', 'Adam');   // Adam, Alexis
o.set({
    'a': 'Alice',     // Alice, Adam
    'b': 'Bob'
});
o.a = undefined;      // undefined, Alice