Background

Currently, most views are can-stache views. Please read stache's documentation to understand how to do things like:

• Write values to the page
• Branching logic
• Looping

This page details the special abilities of a Component's view that are not normally available to a generic stache view.

Use

The view specified by the view property works similar to the W3C Shadow DOM proposal. It represents the contents of a custom element, while being able to reposition the user provided <can-template> elements with <can-slot> elements.

NOTE: Component is also able to reposition with the <content> tag which is no longer favored by the W3C.

There are three things to understand about a component’s view:

• Rendered with a ViewModel - The view is rendered with this as the component instance’s ViewModel.
• View Insertion - The rendered result of the view is inserted into the component’s element.
• <can-slot> elements - Any <can-slot> elements within the view act as insertion points for <can-template> elements.

Rendered with a ViewModel instance

The view is rendered with this as the component instance's ViewModel. For example, the following prints the age property of the ViewModel instance:

import {Component} from "can";

Component.extend({
    tag: "my-component",
    view: `You are {{this.age}}`,
    ViewModel: {
        age: {
            default: 36
        }
    }
});

document.body.innerHTML = "<my-component></my-component>";

Notice that the view is rendered with an instance of the ViewModel, not the ViewModel constructor function. A new ViewModel instance is created for each element. For example, the following shows independent age values:

import {Component} from "can";

Component.extend({
    tag: "my-component",
    view: `You are {{this.age}}`,
    ViewModel: {
        age: {
            value( {resolve} ){
                const timer = setInterval( () => {
                    resolve( Math.round(Math.random() * 100) )
                }, 1000);

                return clearInterval.bind(window, timer);
            }
        }
    }
});

document.body.innerHTML = `<my-component></my-component>.
    <my-component></my-component>.
    <my-component></my-component>.`;

View insertion

The view specified by view is rendered directly within the custom tag.

For example the following component:

Component.extend( {
    tag: "my-greeting",
    view: "<h1>Hello There</h1>"
} );

With the following source html:

<header>
    <my-greeting></my-greeting>
</header>

Produces the following html:

<header>
    <my-greeting><h1>Hello There</h1></my-greeting>
</header>

If there is existing content within the source html, like:

<header>
    <my-greeting>DO REMOVE ME!!!</my-greeting>
</header>

…that content is removed and replaced by the component’s view:

<header>
    <my-greeting><h1>Hello There</h1></my-greeting>
</header>

Use <can-slot> to position content within the source html.

<can-slot> elements

<can-slot> element inserts the content of <can-template> elements passed to the component. This makes customizing the HTML of a component much easier.

For example, the following defines a modal component whose content can be customized with <can-template> and positioned with <can-slot>. Change the text of the input to see it in action.

<my-app></my-app>
<style>
my-modal {
   position: fixed;
   top: 0px;
   left: 0px;
   right: 0px;
   bottom: 0px;
   z-index: 100;
}
.background {
    width: 100%;
    height: 100%;
    background-color: #aCCaef;
    opacity: 0.2;
}
.modal-container {
    left: 50%;
    top: 50%;
    width: 300px;
    height: 300px;
    margin-top: -150px;
    margin-left: -150px;
    position: absolute;
    border: 1px solid #e1e1e8;
    background-color: white;
}
my-modal h3{
    border-bottom: 1px solid #e1e1e8;
    padding-left: 20px;
    padding-bottom: 5px;
}
my-modal .modal-contents {
    padding-left: 20px;
}
</style>
<script type="modal">
import {Component} from "can";

Component.extend({
    tag: "my-modal",
    view: `
        <div class='background'></div>
        <div class='modal-container'>
            <h3>{{this.title}}</h3>
            <div class='modal-contents'>
                <can-slot name="contents"/>
            </div>
        </div>
    `
});

Component.extend({
    tag: "my-app",
    view: `
        {{# if(this.promptSave) }}
            <my-modal title:raw="Wanna Save?">
                <can-template name="contents">
                    <p> Save? </p>
                    <p>
                        <button class='btn btn-primary'
                            on:click="this.save()">Yes</button>
                            <button class='btn btn-warning'
                            on:click="this.cancel()">No</button>
                    </p>
                </can-template>
            </my-modal>
        {{/ if }}
        <div>
            Meetup Name:
            <input value:bind="value" disabled:from="this.saving"/>
            {{# if(this.saving) }} <span class='info'>Saving ...</span> {{/ if }}
        </div>
    `,
    ViewModel: {
        value: "any",
        backup: "any",
        saving: "boolean",

        get promptSave(){
            return !this.saving &&
                this.backup !== this.value;
        },

        save(){
            var self = this;
            this.saving = true;
            setTimeout(() => {
                this.set({
                    saving: false,
                    backup: this.value
                });
            },1000);
        },
        cancel(){
            this.saving = false;
            this.value = this.backup;
        },

        connectedCallback(){
            this.backup = this.value;
        }
    }
});
</script>

Read <can-slot>'s documentation for more information.

Importing Views

The Setting Up CanJS guide has details on how to import stache views directly. For example, the following example uses import view from "./app.stache";:

import { Component } from "can";
import view from "./app.stache";

Component.extend({
  tag: "my-app",
  view,
  ViewModel: {
    message: {
      default: "Hello World"
    }
  }
});

This allows:

• authoring stache files in their own files
• faster load times as the stache files are pre-parsed

Omitting the view

If the view is omitted, the content between the component tags (user DOM) is rendered with the ViewModel. The following renders Hi there! between the <no-view> and </no-view> tags:

<my-app></my-app>
<script type="module">
import { Component } from "can";

Component.extend({
    tag: "no-view",
    ViewModel: {
        message: {default: "Hi there!"}
    }
});

Component.extend({
    tag: "my-app",
    view: `
        <no-view>
            {{this.message}}
        </no-view>
    `
})
</script>