viewModel

Use

can.Component's viewModel property is used to define an object, typically an instance of a can.Map, that will be used to render the component's template. This is most easily understood with an example. The following component shows the current page number based off a limit and offset value:

can.Component.extend({
  tag: "my-paginate",
  viewModel: {
    offset: 0,
    limit: 20,
    page: function(){
      return Math.floor(this.attr('offset') / this.attr('limit')) + 1;
    }
  },
  template: can.stache("Page {{page}}.")
})

If this component HTML was inserted into the page like:

var template = can.stache("<my-paginate/>")
$("body").append(template())

It would result in:

<my-paginate>Page 1</my-paginate>

This is because the provided viewModel object is used to extend a can.Map like:

CustomMap = can.Map.extend({
  offset: 0,
  limit: 20,
  page: function(){
    return Math.floor(this.attr('offset') / this.attr('limit')) + 1;
  }
})

Any primitives found on a can.Map's prototype (ex: offset: 0) are used as default values.

Next, a new instance of CustomMap is created with the attribute data within <my-paginate> (in this case there is none) like:

componentData = new CustomMap(attrs);

And finally, that data is added to the parentScope of the component, used to render the component's template, and inserted into the element:

var newviewModel = parentScope.add(componentData),
    result = can.stache("Page {{page}}.")(newviewModel);
$(element).html(result);

Values passed from attributes

Values can be "passed" into the viewModel of a component, similar to passing arguments into a function. Using can.view.bindings, the following binding types can be setup:

• {to-child} - Update the component's viewModel when the parent scope value changes.
• {^to-parent} - Update the parent scope when the component's viewModel changes.
• {(two-way)} - Update the parent scope or the component's viewModel when the other changes.

As mentioned in the deprecation warning above, using can.stache, values are passed into components like this:

<my-paginate {offset}='index' {limit}='size'></my-paginate>

The above would create an offset and limit property on the component that are initialized to whatever index and size are, NOT two-way bind (between component and parent viewModels) the offset and limit properties to the index and size.

The following component requires an offset and limit:

can.Component.extend({
  tag: "my-paginate",
  viewModel: {
    page: function(){
      return Math.floor(this.attr('offset') / this.attr('limit')) + 1;
    }
  },
  template: can.stache("Page {{page}}.")
});

If <my-paginate>'s source html is rendered like:

var template = can.stache("<my-paginate {offset}='index' {limit}='size'></my-paginate>");

var pageInfo = new can.Map({
  index: 0,
  size: 20
});

$("body").append( template( pageInfo ) );

... pageInfo's index and size are set as the component's offset and limit attributes. If we were to change the value of pageInfo's index like:

pageInfo.attr("index",20)

... the component's offset value will change and its template will update to:

<my-paginate>Page 1</my-paginate>

Using attribute values

You can also pass a literal string value of the attribute. To do this in can.stache, simply pass any value not wrapped in single brackets, and the viewModel property will be initialized to this string value:

<my-tag title="hello"></my-tag>

The above will create a title property in the component's viewModel, which has a string hello.

If the tag's title attribute is changed, it updates the viewModel property automatically. This can be seen in the following example:

Clicking the Change title button sets a <panel> element's title attribute like:

$("#out").on("click", "button", function(){
  $("panel:first").attr("title", "Users")
  $(this).remove();
});

Calling methods on viewModel from events within the template

Using html attributes like can-EVENT-METHOD, you can directly call a viewModel method from a template. For example, we can make <my-paginate> elements include a next button that calls the viewModel's next method like:

can.Component.extend({
  tag: "my-paginate",
  viewModel: {
    offset: 0,
    limit: 20,
    next: function(context, el, ev){
      this.attr("offset", this.offset + this.limit);
    },
    page: function(){
      return Math.floor(this.attr('offset') / this.attr('limit')) + 1;
    }
  },
  template: can.stache("Page {{page}} <button ($click)='next()'>Next</button>")
})

viewModel methods get called back with the current context, the element that you are listening to and the event that triggered the callback.

Publishing events on viewModels

Maps can publish events on themselves. For instance, the following <player-edit> component, dispatches a "close" event when it's close method is called:

can.Component.extend({
  tag: "player-edit",
  template: can.view('player-edit-stache'),
  viewModel: {
    close: function(){
      this.dispatch("close");
    }
  }
});

These can be listened to with (event) bindings like:

<player-edit 
    (close)="removeEdit()" 
    {player}="editingPlayer"/>

The following demo uses this ability to create a close button that hides the player editor: