events

Listen to events on elements and observables.

`Object<eventDescription,eventHandler(element, event)()>`

An object of event names and methods that handle the event. For example:

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:

Components have the ability to bind to special inserted and removed events that are called when a component’s tag has 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
    }
  }

High performance view rendering

While can-stache-bindings conveniently allows you to call a ViewModel method from a view like:

<input ($change)="doSomething()"/>

This has the effect of binding an event handler directly to this element. Every element that has a ($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.