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Listen to events on elements and observables.
Deprecated 4.0
For elements, use the on:event syntax to attach event listeners directly to elements instead. For observables, use listenTo within connectedCallback instead.
Object<eventDescription,eventHandler(element, event)()>
An object of event names and methods that handle the event. For example:
import Component from "can-component";
Component.extend( {
ViewModel: {
limit: "number",
offset: "number",
next: function() {
this.offset = this.offset + this.limit;
}
},
events: {
".next click": function() {
this.viewModel.next();
},
"{viewModel} limit": function( viewModel, ev, newValue ) {
console.log( "limit is now", newValue );
}
}
} );
A component’s events object is used as the prototype of a can-control. The control gets created on the component’s element.
The component’s ViewModel instance is available within event handlers as this.viewModel.
The component element is available as this.element.
Use
can-component’s events object allows you to provide low-level can-control-like abilities to a Component
while still accessing the Component’s ViewModel. The following
example listens to clicks on elements with className="next" and calls .next() on the component’s viewModel.
The events object can also listen to objects or properties on the component’s ViewModel instance. For instance, instead of using live-binding, we could listen to when offset changes and update the page manually:
Special events: inserted and removed
In previous versions of CanJS, components had the ability to bind to special
inserted and removed events that were called when a component’s element had
been inserted into or removed from the page:
{
events: {
"inserted": function() {
// called when the component’s tag is inserted into the DOM
},
"removed": function() {
// called when the component’s tag is removed from the DOM
}
}
}
You can still bind to these special events by using the can-3-4-compat package, but this is deprecated in favor of the new connectedCallback API. See more information about migrating away from the inserted and removed events in the Migrating to CanJS 4 guide.
High performance view rendering
While can-stache-bindings conveniently allows you to call a ViewModel method from a view like:
<input on:change="doSomething()"/>
This has the effect of binding an event handler directly to this element. Every element that has a on:click or similar attribute has an event handler bound to it. For a large grid or list, this could have a performance penalty.
By contrast, events bound using can-component’s events object use event delegation, which is useful for high performance view rendering. In a large grid or list, event delegation only binds a single event handler rather than one per row.