@dojo/widget-core

widget-core is a library to create powerful, composable user interface widgets.

Reactive & unidirectional: widget-core follows core reactive principles to ensure predictable, consistent behavior.
Encapsulated Widgets: Create independent encapsulated widgets that can be wired together to create complex and beautiful user interfaces.
DOM Abstractions: widget-core provides API abstractions to avoid needing to access or manipulate the DOM outside of the reactive render life-cycle.
I18n & Themes: widget-core provides core mixins to enable internationalization and theming support for your widgets.

Installation
Features
Key Principles
Advanced Concepts
How Do I Contribute?
- Setup Installation
- Testing
Licensing Information

Installation

To use @dojo/widget-core, install the package along with its required peer dependencies:

npm install @dojo/widget-core

# peer dependencies
npm install @dojo/has
npm install @dojo/shim
npm install @dojo/core
npm install @dojo/i18n

You can also use the dojo cli to create a complete Dojo 2 skeleton application.

Features

Basic Widgets

Dojo 2 applications use the Virtual DOM (vdom) paradigm to represent what should be shown on the view. These vdom nodes are plain JavaScript objects that are more efficient to create from a performance perspective than browser DOM elements. Dojo 2 uses these vdom elements to synchronize and update the browser DOM so that the application shows the expected view.

There are two types of vdom within Dojo 2, the first are pure representations of DOM elements and are the fundamental building blocks of all Dojo 2 applications. These are called HNodes and are created using the v() function available from the @dojo/widget-core/d module.

The following will create a HNode that represents a simple div DOM element, with a text node child: Hello, Dojo 2!:

v('div', [ 'Hello, Dojo 2!' ])

The second vdom type, WNode, represent widgets. A widget is a class that extends WidgetBase from @dojo/widget-core/WidgetBase and implements a render function that returns one of the Dojo 2 vdom types (known as a DNode). Widgets are used to represent reusable, independent sections of a Dojo 2 application.

The following returns the HNode example from above from the render function:

class HelloDojo extends WidgetBase {
    protected render() {
        return v('div', [ 'Hello, Dojo 2!' ]);
    }
}

Rendering a Widget in the DOM

To display your new component in the view you will need to decorate it with some functionality needed to "project" the widget into the browser. This is done using the ProjectorMixin from @dojo/widget-core/mixins/Projector.

const Projector = ProjectorMixin(HelloDojo);
const projector = new Projector();

projector.append();

By default the projector will attach the widget to the document.body in the DOM, but this can be overridden by passing a reference to the preferred parent DOM Element.

Consider the following in your HTML file:

<div id="my-app"></div>

You can target this Element:

const root = document.getElementById('my-app');
const Projector = ProjectorMixin(HelloDojo);
const projector = new Projector();

projector.append(root);

Widgets and Properties

We have created a widget used to project our HNodes into the DOM, however widgets can be composed of other widgets and properties which are used to determine if a widget needs to be re-rendered.

Properties are available on the the widget instance, defined by an interface and passed as a generic to the WidgetBase class when creating your custom widget. The properties interface should extend the base WidgetProperties provided from @dojo/widget-core/interfaces:

interface MyProperties extends WidgetProperties {
    name: string;
}

class Hello extends WidgetBase<MyProperties> {
    protected render() {
        const { name } = this.properties;

        return v('div', [ `Hello, ${name}` ]);
    }
}

New properties are compared with the previous properties to determine if a widget requires re-rendering. By default Dojo 2 uses the auto diffing strategy, that performs a shallow comparison for objects and arrays, ignores functions (except classes that extend WidgetBase) and a reference comparison for all other values.

Composing Widgets

As mentioned, often widgets are composed of other widgets in their render output. This promotes widget reuse across an application (or multiple applications) and promotes widget best practices.

To compose widgets, we need to create WNodes and we can do this using the w() function from @dojo/widget-core/d.

Consider the previous Hello widget that we created:

class App extends WidgetBase {
    protected render() {
        return v('div', [
            w(Hello, { name: 'Bill' }),
            w(Hello, { name: 'Bob' }),
            w(Hello, { name: 'Flower pot men' })
        ]);
    }
}

We can now use App with the ProjectorMixin to render the Hello widgets.

const Projector = ProjectorMixin(App);
const projector = new Projector();

projector.append();

Note: Widgets must return a single top level DNode from the render method, which is why the Hello widgets were wrapped in a div element.

Decomposing Widgets

Splitting widgets into multiple smaller widgets is easy and helps to add extended functionality and promotes reuse.

Consider the following List widget, which has a simple property interface of an array of items consisting of content: string and highlighted: boolean.

interface ListProperties {
    items: {
        id: string;
        content: string;
        highlighted: boolean;
    };
}

class List extends WidgetBase<ListProperties> {
    protected render() {
        const { items } = this.properties;

        return v('ul', { classes: 'list' }, items.map((item) => {
            const { id, highlighted, content } = item;
            const classes = [ highlighted ? 'highlighted' : null ];

            return v('li', { key: id, classes }, [ content ]);
        });
    }
}

The List widget works as expected and displays the list in the browser but is difficult to reuse, modify, and/or extend.

Note: When working with children arrays with the same type of widget or Element, it is important to add a unique key property or attribute so that Dojo 2 can identify the correct node when updates are made.

To extend the List API with an event that needs to be called when an item is clicked with the item's id, we first update the properties interface:

interface ListProperties {
    items: {
        id: string;
        content: string;
        highlighted: boolean;
    };
    onItemClick: (id: string) => void;
}

If we try to use the onItemClick function in the current List widget, we would need to wrap it in another function in order to pass the item's id.

This would mean a new function would be created every render but Dojo 2 does not support changing listener functions after the first render and this would error.

To resolve this, the list item can be extracted into a separate widget:

interface ListItemProperties {
    id: string;
    content: string;
    highlighted: boolean;
    onItemClick: (id: string) => void;
}

class ListItem extends WidgetBase<ListItemProperties> {

    protected onClick(event: MouseEvent) {
        const { id } = this.properties;

        this.properties.onItemClick(id);
    }

    protected render() {
        const { id, content, highlighted } = this.properties;
        const classes = [ highlighted ? 'highlighted' : null ];

        return v('li', { key: id, classes, onclick: this.onClick }, [ content ]);
    }
}

Using the ListItem we can simplify the List slightly and also add the onclick functionality that we required:

interface ListProperties {
    items: {
        id: string;
        content: string;
        highlighted: boolean;
    };
    onItemClick: (id: string) => void;
}

class List extends WidgetBase<ListProperties> {
    protected render() {
        const { onItemClick, items } = this.properties;

        return v('ul', { classes: 'list' }, items.map(({ id, content, highlighted }) => {
            return w(ListItem, { key:id, content, highlighted, onItemClick });
        });
    }
}

Additionally the ListItem is now reusable in other areas of our application(s).

Mixins

Dojo 2 makes use of mixins to decorate additional functionality and properties to existing widgets. Mixins provide a mechanism that allows loosely coupled design and composition of behaviors into existing widgets without having to change the base widget.

TypeScript supports mixins using a constructor type of new (...args: any[]) => any; that enables a class to be passed as a function argument and extended to add new functionality.

Example mixin that adds method setState and readonly state property:

// interface for the extended API
interface StateMixin {
    readonly state: Readonly<any>;
    setState(state: any): void;
}

// function that accepts a class that extends `WidgetBase` and returns the extended class with the `StateMixin`
// behavior
function StateMixin<T extends new(...args: any[]) => WidgetBase>(Base: T): T & (new(...args: any[]) => StateMixin) {
    return class extends Base {
        private _state: any;

        public setState(state: any): void {
            // shallow copy of the state
            this._state = { ...this._state, ...state };
            // invalidate the widget
            this.invalidate();
        }

        public get state(): any {
            return this._state;
        }
    };
}

Examples of Dojo 2 mixins can be seen with ThemedMixin and I18nMixin that are described in Classes & theming and Internationalization sections.

Animation

Dojo 2 widget-core provides a WebAnimation meta to apply web animations to VNodes.

To specify the web animations pass an AnimationProperties object to the WebAnimation meta along with the key of the node you wish to animate. This can be a single animation or an array or animations.

Basic Example

export default class AnimatedWidget extends WidgetBase {
    protected render() {
        const animate = {
            id: 'rootAnimation',
            effects: [
                { height: '10px' },
                { height: '100px' }
            ],
            controls: {
                play: true
            }
        };

        this.meta(WebAnimation).animate('root', animate);

        return v('div', {
            key: 'root'
        });
    }
}

controls and timing are optional properties and are used to setup and control the animation. The timing property can only be set once, but the controls can be changed to stop / start / reverse etc... the web animation.

Changing Animation

Animations can be changed on each widget render in a reactive pattern, for example changing the animation from slideUp to slideDown on a title pane depending of if the titlepane is open or not.

export default class AnimatedWidget extends WidgetBase {
    private _open = false;

    protected render() {
        const animate = this._open ? {
            id: 'upAnimation',
            effects: [
                { height: '100px' },
                { height: '0px' }
            ],
            controls: {
                play: true
            }
        } : {
            id: 'downAnimation',
            effects: [
                { height: '0px' },
                { height: '100px' }
            ],
            controls: {
                play: true
            }
        };

        this.meta(WebAnimation).animate('root', animate);

        return v('div', {
            key: 'root'
        })
    }
}

Passing an effects function

An effects function can be passed to the animation and evaluated at render time. This allows you to create programatic effects such as those depending on measurements from the Dimensions Meta.

export default class AnimatedWidget extends WidgetBase {
    private _getEffect() {
        const { scroll } = this.meta(Dimensions).get('content');

        return [
            { height: '0px' },
            { height: `${scroll.height}px` }
        ];
    }

    protected render() {
        const animate = {
            id: 'upAnimation',
            effects: this._getEffect(),
            controls: {
                play: true
            }
        };

        this.meta(WebAnimation).animate('root', animate);

        return v('div', {
            key: 'root'
        })
    }
}

Get animation info

The WebAnimation meta provides a get function that can be used to retrieve information about an animation via it's id. This info contains the currentTime, playState, playbackRate and startTime of the animation. If no animation is found or the animation has been cleared this will return undefined.

export default class AnimatedWidget extends WidgetBase {
    protected render() {
        const animate = {
            id: 'rootAnimation',
            effects: [
                { height: '10px' },
                { height: '100px' }
            ],
            controls: {
                play: true
            }
        };

        this.meta(WebAnimation).animate('root', animate);

        const info = this.meta(WebAnimation).get('rootAnimation');

        return v('div', {
            key: 'root'
        });
    }
}

Styling & Theming

Overview

Dojo 2 widget-core provides ThemedMixin to decorate a widget with theming functionality and a @theme decorator to specify the classes available to the widget. Both ThemedMixin and @theme are provided by @dojo/widget-core/mixins/Themed.

To specify the theme classes for a widget, an interface needs to be imported with named exports for each class and passed to the @theme decorator. Importing the interface provides IntelliSense / auto-complete for the class names and passing this via the @theme decorator informs the ThemedMixin which classes can be themed.

Example css classes interface

export const classNameOne: string;
export const classNameTwo: string;

Important: at runtime a JavaScript file is required to provide the processed CSS class names.

The ThemedMixin provides a method available on the instance this.theme() takes a single argument that is either a string class name or an array of string class names and returns the theme's equivalent class names as either a single string or array of strings.

However, it is not always desirable to allow consumers to override styling that may be required for a widget to function correctly. These classes can be added directly to the classes array in VirtualDomProperties.

The following example passes css.root that will be themeable and css.rootFixed that cannot be overridden.

import * as css from './styles/myWidget.m.css';
import { ThemeableMixin, theme } from '@dojo/widget-core/mixins/Themeable';

@theme(css)
export default class MyWidget extends ThemeableMixin(WidgetBase) {
    protected render() {
        return v('div', { classes: [ this.theme(css.root), css.rootFixed ] });
    }
}

If an array is passed to this.theme then an array will be returned. For example, this.theme([ css.root, css.other ]) will return an array containing the theme's class names [ 'themedRoot', 'themedOther' ].

Writing a theme

Themes are TypeScript modules that export an object that contains css-modules files keyed by a widgets CSS file name.

/* myTheme/styles/myWidget.m.css */
.root {
    color: blue;
}

// myTheme/theme.ts
import * as myWidget from './styles/myWidget.m.css';

export default {
    'myWidget': myWidget
}

In the above example, the new root class provided by the theme for myWidget will replace the root class that was provided by the original myWidget.m.css. This means the myWidget will now have its color set to blue, but will no longer receive the styles from the root class in the original CSS.

Applying a theme

To apply a theme to a widget, simply require it as a module and pass it to a widget via its properties. It is important to ensure that any child widgets created within your widget's render function are passed the theme or they will not be themed.

// app.ts
import myTheme from './myTheme/theme';

// ...
render() {
    return w(TabPanel, { theme: myTheme } });
}

Passing extra classes

Sometimes you may need to apply positioning or layout styles to a child widget. As it is not possible to pass classes directly to virtualized widget nodes. WNodes thus provide an extraClasses property to target themeable classes within its render function. In most cases this should only target the root class and apply positioning adjustments. The classes passed via extraClasses are outside of the theming mechanism and thus will not be effected by a change in theme.

/* app.m.css */
.tabPanel {
    position: absolute;
    left: 50px;
    top: 50px;
}

// app.ts
import * as appCss from './styles/app.m.css';

// ...
render() {
    return w(TabPanel, { extraClasses: { 'root': appCss.tabPanel } });
}

In the above example, the tabPanel will receive its original root class in addition to the appCss.tabPanel class when used with this.theme.

Internationalization

Widgets can be internationalized by adding the I18nMixin mixin from @dojo/widget-core/mixins/I18n. Message bundles are localized by passing them to localizeBundle.

If the bundle supports the widget's current locale, but those locale-specific messages have not yet been loaded, then the default messages are returned. The widget will be invalidated once the locale-specific messages have been loaded, triggering a re-render with the localized message content.

Each widget can have its own locale by passing a property - properties.locale. If no locale is set, then the default locale, as set by @dojo/i18n, is assumed.

const MyWidgetBase = I18nMixin(WidgetBase);

class I18nWidget extends MyWidgetBase<I18nWidgetProperties> {
    render() {
        // Load the "greetings" messages for the current locale. If the locale-specific
        // messages have not been loaded yet, then the default messages are returned,
        // and the widget will be invalidated once the locale-specific messages have
        // loaded.
        const messages = this.localizeBundle(greetingsBundle);

        return v('div', { title: messages.hello }, [
            w(Label, {
                // Passing a message string to a child widget.
                label: messages.purchaseItems
            }),
            w(Button, {
                // Passing a formatted message string to a child widget.
                label: messages.format('itemCount', { count: 2 })
            })
        ]);
    }
}

Key Principles

These are some of the important principles to keep in mind when creating and using widgets:

The widget's __render__, __setProperties__, __setChildren__ functions should never be called or overridden.
- These are the internal methods of the widget APIs and their behavior can change in the future, causing regressions in your application.
Except for projectors, you should never need to deal directly with widget instances
- The Dojo 2 widget system manages all instances required including caching and destruction, trying to create and manage other widgets will cause issues and will not work as expected.
Never update properties within a widget instance, they should be considered pure.
- Properties are considered read-only and should not be updated within a widget instance, updating properties could cause unexpected behavior and introduce bugs in your application.
Hyperscript should always be written using the @dojo/widget-core/d#v() function.
- The widget-core abstraction for Hyperscript is the only type of vdom that widget-core can process for standard DOM elements, any other mechanism will not work properly or at all.

Advanced Concepts

This section provides some details on more advanced Dojo 2 functionality and configuration that may be required to build more complex widgets and applications.

Advanced Properties

Controlling the diffing strategy can be done at an individual property level using the diffProperty decorator on a widget class.

widget-core provides a set of diffing strategy functions from @dojo/widget-core/diff.ts that can be used. When these functions do not provide the required functionality a custom diffing function can be provided. Properties that have been configured with a specific diffing type will be excluded from the automatic diffing.

Diff Function	Description
`always`	Always report a property as changed.
`auto`	Ignore functions (except classes that extend `WidgetBase`), shallow compare objects, and reference compare all other values.
`ignore`	Never report a property as changed.
`reference`	Compare values by reference (`old === new`)
`shallow`	Treat the values as objects and compare their immediate values by reference.

Important: All diffing functions should be pure functions and are called WITHOUT any scope.

// using a diff function provided by widget-core#diff
@diffProperty('title', reference)
class MyWidget extends WidgetBase<MyProperties> { }

//custom diff function; A pure function with no side effects.
function customDiff(previousProperty: string, newProperty: string): PropertyChangeRecord {
    return {
        changed: previousProperty !== newProperty,
        value: newProperty
    };
}

// using a custom diff function
@diffProperty('title', customDiff)
class MyWidget extends WidgetBase<MyProperties> { }

Property Diffing Reactions

It can be necessary to perform some internal logic when one or more properties change, this can be done by registering a reaction callback.

A reaction function is registered using the diffProperty decorator on a widget class method. This method will be called when the specified property has been detected as changed and receives both the old and new property values.

class MyWidget extends WidgetBase<MyProperties> {

    @diffProperty('title', auto)
    protected onTitleChange(previousProperties: any, newProperties: any): void {
        this._previousTitle = previousProperties.title;
    }
}

diffProperty decorators can be stacked on a single class method and will be called if any of the specified properties are considered changed.

class MyWidget extends WidgetBase<MyProperties> {

    @diffProperty('title', auto)
    @diffProperty('subtitle', auto)
    protected onTitleOrSubtitleChange(previousProperties: any, newProperties: any): void {
        this._titlesUpdated = true;
    }
}

For non-decorator environments (Either JavaScript/ES6 or a TypeScript project that does not have the experimental decorators configuration set to true in the tsconfig), the functions need to be registered in the constructor using the addDecorator API with diffProperty as the key.

class MyWidget extends WidgetBase {

    constructor() {
        super();
        diffProperty('foo', auto, this.diffFooReaction)(this);
    }

    diffFooReaction(previousProperty: any, newProperty: any) {
        // do something to reaction to a diff of foo
    }
}

Registry

The Registry provides a mechanism to define widgets and injectors (see the Containers & Injectors section), that can be dynamically/lazily loaded on request. Once the registry widget is loaded all widgets that need the newly loaded widget will be invalidated and re-rendered automatically.

A main registry can be provided to the projector, which will be automatically passed to all widgets within the tree (referred to as baseRegistry). Each widget also gets access to a private Registry instance that can be used to define registry items that are scoped to the widget. The locally defined registry items are considered a higher precedence than an item registered in the baseRegistry.

import { Registry } from '@dojo/widget-core/Registry';

import { MyWidget } from './MyWidget';
import { MyInjector } from './MyInjector';

const registry = new Registry();
registry.define('my-widget', MyWidget);
registry.defineInjector('my-injector', MyInjector);
// ... Mixin and create Projector ...

projector.setProperties({ registry });

In some scenarios, it might be desirable to allow the baseRegistry to override an item defined in the local registry. Use true as the second argument of the registry.get function to override the local item.

The Registry will automatically detect and handle widget constructors as default exports for imported esModules for you.

Registry Decorator

A registry decorator is provided to make adding widgets to a local registry easier. The decorator can be stacked to register multiple entries.

// single entry
@registry('loading', LoadingWidget)
class MyWidget extends WidgetBase {
    render() {
        if (this.properties) {
            const LoadingWidget = this.registry.get('loading', true);
            return w(LoadingWidget, {});
        }
        return w(MyActualChildWidget, {});
    }
}

// multiple entries
@registry('loading', LoadingWidget)
@registry('heading', () => import('./HeadingWidget'))
class MyWidget extends WidgetBase {
    render() {
        if (this.properties) {
            const LoadingWidget = this.registry.get('loading', true);
            return w(LoadingWidget, {});
        }
        return w(MyActualChildWidget, {}, [
            w('heading', {})
        ]);
    }
}

Loading esModules

The registry can handle the detection of imported esModules for you that have the widget constructor as the default export. This means that your callback function can simply return the import call. If the widget constructor is not the default export you will need to pass it manually.

@registry('Button', () => import('./Button')) // default export
@registry('Table', async () => {
    const module = await import('./HeadingWidget');
    return module.table;
})
class MyWidget extends WidgetBase {}

Decorator Lifecycle Hooks

Occasionally, in a mixin or a widget class, it my be required to provide logic that needs to be executed before properties are diffed using beforeProperties, either side of a widget's render call using beforeRender & afterRender or after a constructor using afterContructor.

This functionality is provided by the beforeProperties, beforeRender, afterRender and afterConstructor decorators that can be found in the decorators directory.

Note: All lifecycle functions are executed in the order that they are specified from the super class up to the final class.

beforeProperties

The beforeProperties lifecycle hook is called immediately before property diffing is executed. Functions registered for beforeProperties receive properties and are required to return any updated, changed properties that are mixed over (merged) the existing properties.

As the lifecycle is executed before the property diffing is completed, any new or updated properties will be included in the diffing phase.

An example that demonstrates adding an extra property based on the widgets current properties, using a function declared on the widget class myBeforeProperties:

class MyClass extends WidgetBase<MyClassProperties> {

    @beforeProperties()
    protected myBeforeProperties(properties: MyClassProperties): MyClassProperties {
        if (properties.type = 'myType') {
            return { extraProperty: 'foo' };
        }
        return {};
    }
}

AlwaysRender

The alwaysRender decorator is used to force a widget to always render regardless of whether the widget's properties are considered different.

@alwaysRender()
class MyClass extends WidgetBase {}

BeforeRender

The beforeRender lifecycle hook receives the widget's render function, properties and children and is expected to return a function that satisfies the render API. The properties and children are passed to enable them to be manipulated or decorated prior to render being called.

Note: When properties are changed during the beforeRender lifecycle, they do not go through the standard property diffing provided by WidgetBase. If the changes to the properties need to go through diffing, consider using the beforeProperties lifecycle hook.

class MyClass extends WidgetBase {

    @beforeRender()
    protected myBeforeRender(renderFunc: () => DNode, properties: any, children: DNode[]): () => DNode {
        // decorate/manipulate properties or children.
        properties.extraAttribute = 'foo';
        // Return or replace the `render` function
        return () => {
            return v('my-replaced-attribute');
        };
    }
}

AfterRender

The afterRender lifecycle hook receives the returned DNodes from a widget's render call, so that the nodes can be decorated, manipulated or swapped completely.

class MyBaseClass extends WidgetBase<WidgetProperties> {
    @afterRender()
    myAfterRender(result: DNode): DNode {
        // do something with the result
        return result;
    }
}

Method Lifecycle Hooks

These lifecycle hooks are used by overriding methods in a widget class. Currently onAttach and onDetach are supported and provide callbacks for when a widget has been first attached and removed (destroyed) from the virtual dom.

onAttach

onAttach is called once when a widget is first rendered and attached to the DOM.

class MyClass extends WidgetBase {
    onAttach() {
        // do things when attached to the DOM
    }
}

onDetach

onDetach is called when a widget is removed from the widget tree and therefore the DOM. onDetach is called recursively down the tree to ensure that even if a widget at the top of the tree is removed all the child widgets onDetach callbacks are fired.

class MyClass extends WidgetBase {
    onDetach() {
        // do things when removed from the DOM
    }
}

Containers & Injectors

There is built in support for side-loading/injecting values into sections of the widget tree and mapping them to a widget's properties. This is achieved by registering a @dojo/widget-core/Injector instance against a registry that is available to your application (i.e. set on the projector instance, projector.setProperties({ registry })).

Create an Injector instance and pass the payload that needs to be injected to the constructor:

const injector = new Injector({ foo: 'baz' });
registry.defineInjector('my-injector', injector);

To connect the registered injector to a widget, we can use the Container HOC (higher order component) provided by widget-core. The Container accepts a widget constructor, injector label and getProperties mapping function as arguments and returns a new class that returns the passed widget from its render function.

getProperties receives the payload from an injector and properties from the container HOC component. These are used to map into the wrapped widgets properties.

import { Container } from '@dojo/widget-core/Container';
import { MyWidget } from './MyWidget';

function getProperties(payload: any, properties: any) {
    return {
        foo: payload.foo
    };
}

export const MyWidgetContainer = Container(MyWidget, 'my-injector', getProperties);

The returned class from Container HOC is then used in place of the widget it wraps, the container assumes the properties type of the wrapped widget, however they all considered optional.

// import { MyWidget } from './MyWidget';
import { MyWidgetContainer } from './MyWidgetContainer';

interface AppProperties {
    foo: string;
}

class App extends WidgetBase<AppProperties> {
    render() {
        return v('div', {}, [
            // w(MyWidget, { foo: 'bar' })
            w(MyWidgetContainer, {})
        ]);
    }
}

Decorators

All core decorators provided by widget-core, can be used in non-decorator environments (Either JavaScript/ES6 or a TypeScript project that does not have the experimental decorators configuration set to true in the tsconfig) programmatically by calling them directly, usually within a Widget class' constructor.

Example usages:

constructor() {
    beforeProperties(this.myBeforeProperties)(this);
    beforeRender(myBeforeRender)(this);
    afterRender(this.myAfterRender)(this);
    diffProperty('myProperty', this.myPropertyDiff)(this);
}

`DOMWrapper`

DomWrapper is used to wrap DOM that is created outside of the virtual DOM system. This is the main mechanism to integrate foreign components or widgets into the virtual DOM system.

The DomWrapper generates a class/constructor function that is then used as a widget class in the virtual DOM. DomWrapper takes up to two arguments. The first argument is the DOM node that it is wrapping. The second is an optional set of options.

The currently supported options:

Name	Description
`onAttached`	A callback that is called when the wrapped DOM is flowed into the virtual DOM

For example, if we want to integrate a third-party library where we need to pass the component factory a root element and then flow that into our virtual DOM. In this situation we do not want to create the component until the widget is being flowed into the DOM, so onAttached is used to perform the creation of the component:

import { w } from '@dojo/widget-core/d';
import DomWrapper from '@dojo/widget-core/util/DomWrapper';
import WidgetBase from '@dojo/widget-core/WidgetBase';
import createComponent from 'third/party/library/createComponent';

export default class WrappedComponent extends WidgetBase {
    private _component: any;
    private _onAttach = () => {
        this._component = createComponent(this._root);
    }
    private _root: HTMLDivElement;
    private _WrappedDom: DomWrapper;

    constructor() {
        super();
        const root = this._root = document.createElement('div');
        this._WrappedDom = DomWrapper(root, { onAttached: this._onAttached });
    }

    public render() {
        return w(this._WrappedDom, { key: 'wrapped' });
    }
}

The properties which can be set on DomWrapper are the combination of the WidgetBaseProperties and the VirtualDomProperties, which means effectively you can use any of the properties passed to a v() node and they will be applied to the wrapped DOM node. For example the following would set the classes on the wrapped DOM node:

const div = document.createElement('div');
const WrappedDiv = DomWrapper(div);
const wNode = w(WrappedDiv, {
    classes: [ 'foo' ]
});

Meta Configuration

Widget meta is used to access additional information about the widget, usually information only available through the rendered DOM element - for example, the dimensions of an HTML node. You can access and respond to meta data during a widget's render operation.

class TestWidget extends WidgetBase<WidgetProperties> {
    render() {
        const dimensions = this.meta(Dimensions).get('root');

        return v('div', {
            key: 'root',
            innerHTML: `Width: ${dimensions.width}`
        });
    }
}

If an HTML node is required to calculate the meta information, a sensible default will be returned and your widget will be automatically re-rendered to provide more accurate information.

Dimensions

The Dimensions meta provides size/position information about a node.

const dimensions = this.meta(Dimensions).get('root');

In this simple snippet, dimensions would be an object containing offset, position, scroll, and size objects.

The following fields are provided:

Property	Source
`position.bottom`	`node.getBoundingClientRect().bottom`
`position.left`	`node.getBoundingClientRect().left`
`position.right`	`node.getBoundingClientRect().right`
`position.top`	`node.getBoundingClientRect().top`
`size.width`	`node.getBoundingClientRect().width`
`size.height`	`node.getBoundingClientRect().height`
`scroll.left`	`node.scrollLeft`
`scroll.top`	`node.scrollTop`
`scroll.height`	`node.scrollHeight`
`scroll.width`	`node.scrollWidth`
`offset.left`	`node.offsetLeft`
`offset.top`	`node.offsetTop`
`offset.width`	`node.offsetWidth`
`offset.height`	`node.offsetHeight`

If the node has not yet been rendered, all values will contain 0. If you need more information about whether or not the node has been rendered you can use the has method:

const hasRootBeenRendered = this.meta(Dimensions).has('root');

Drag

The Drag meta allow a consuming widget to determine if its nodes are being dragged and by how much. The meta provider abstracts away the need of dealing with modelling specific mouse, pointer, and touch events to create a drag state.

const dragResult = this.meta(Drag).get('root');

The drag information returned contains the following properties:

Property	Description
`delta`	An `x`/`y` position that contains the number of pixels the pointer has moved since the last read of the drag state.
`isDragging`	If the pointer is currently active in dragging the identified node.
`start`	A position object that contains `x`/`y` positions for `client`, `offset`, `page`, and `screen` that provides the start positions that the `delta` movement refers to. Note that `offset` and `page` are not supprted by all browsers and the meta provider does nothing to normalize this data, it simply copies it from the underlying events.

One common use case it to create a draggable node within a container:

interface ExampleWidget extends WidgetBaseProperties {
    height: number;
    top: number;
    onScroll?(delta: number): void;
}

class VerticalScrollBar extends WidgetBase {
    protected render() {
        const { height, top, onScroll } = this.properties;
        const dragResult = this.meta(Drag).get('slider');
        onScroll && onScroll(dragResult.delta.y);
        return v('div', {
            classes: [ css.root, dragResult.isDragging ? css.dragging : null ],
            key: 'root'
        }, [
            v('div', {
                classes: [ css.slider ],
                key: 'slider',
                styles: {
                    height: `${height}px`,
                    top: `${top}px`
                }
            })
        ])
    }
}

class VerticalScrollBarController extends WidgetBase {
    private _top: 0;
    private _onScroll(delta: number) {
        this._top += delta;
        if (this._top < 0) {
            this._top = 0;
        }
        this.invalidate();
    }

    protected render() {
        return w(VerticalScrollBar, {
            top: this._top,
            width: 10,
            onScroll: this._onScroll
        });
    }
}

As can be seen in the above code, the meta provider simply provides information which the widgets can react to. The implementation needs to react to these changes.

Focus

The Focus meta determines whether a given node is focused or contains document focus. Calling this.meta(Focus).get(key) returns the following results object:

Property	Description
`active`	A boolean indicating whether the specified node itself is focused.
`containsFocus`	A boolean indicating whether one of the descendants of the specified node is currently focused. This will return true if `active` is true.

An example usage that opens a tooltip if the trigger is focused might look like this:

class MyWidget extends WidgetBase<WidgetProperties> {
    // ...
    render() {
        // run your meta
        const buttonFocus = this.meta(FocusMeta).get('button');
        return v('div', {
          w(Button, {
            key: 'button'
          }, [ 'Open Tooltip' ]),
          w(Tooltip, {
            content: 'Foo',
            open: buttonFocus.active
          }, [ 'modal content' ])
        });
    }
    // ...
}

The Focus meta also provides a set method to call focus on a given node. This is most relevant when it is necessary to shift focus in response to a user action, e.g. when opening a modal or navigating to a new page. You can use it like this:

class MyWidget extends WidgetBase<WidgetProperties> {
    // ...
    render() {
        // run your meta
        return v('div', {
          w(Button, {
            onClick: () => {
              this.meta(Focus).set('modal');
            }
          }, [ 'Open Modal' ]),
          v('div', {
            key: 'modal',
            tabIndex: -1
          }, [ 'modal content' ])
        });
    }
    // ...
}

Matches

The Matches meta determines if the target of a DOM event matches a particular virtual DOM key.

const matches = this.meta(Matches).get('root', evt);

This allows a widget to not have to know anything about the real DOM when dealing with events that may have bubbled up from child DOM. For example to determine if the containing node in the widget was clicked on, versus the child node, you would do something like this:

class TestWidget extends WidgetBase<WidgetProperties> {
    private _onclick(evt: MouseEvent) {
        if (this.meta(Matches).get('root', evt)) {
            console.log('The root node was clicked on.');
        }
    }

    render() {
        const dimensions = this.meta(Matches).get('root');

        return v('div', {
            key: 'root'
            onclick: this._onclick
        }, [
            v('div', {
                innerHTML: 'Hello World'
            })
        ]);
    }
}

Implementing Custom Meta

You can create your own meta if you need access to DOM nodes.

import MetaBase from "@dojo/widget-core/meta/Base";

class HtmlMeta extends MetaBase {
    get(key: string): string {
        const node = this.getNode(key);
        return node ? node.innerHTML : '';
    }
}

And you can use it like:

class MyWidget extends WidgetBase<WidgetProperties> {
    // ...
    render() {
        // run your meta
        const html = this.meta(HtmlMeta).get('comment');

        return v('div', { key: 'comment', innerHTML: html });
    }
    // ...
}

Extending the base class found in meta/Base will provide the following functionality:

has - A method that accepts a key and returns a boolean to denote if the corresponding node exists in the rendered DOM.
getNode - A method that accepts a key string to inform the widget it needs a rendered DOM element corresponding to that key. If one is available, it will be returned immediately. If not, a callback is created which will invalidate the widget when the node becomes available. This uses the underlying nodeHandler event system.
invalidate - A method that will invalidate the widget.
afterRender - This provides a hook into the widget afterRender lifecycle that can be used to clear up any resources that the meta has created. This is used, for instance, in the WebAnimation meta to clear down unused animations.

Meta classes that require extra options should accept them in their methods.

import MetaBase from "@dojo/widget-core/meta/Base";

interface IsTallMetaOptions {
    minHeight: number;
}

class IsTallMeta extends MetaBase {
    isTall(key: string, { minHeight }: IsTallMetaOptions = { minHeight: 300 }): boolean {
        const node = this.getNode(key);
        if (node) {
            return node.offsetHeight >= minHeight;
        }
        return false;
    }
}

JSX Support

In addition to creating widgets functionally using the v() and w() functions from @dojo/widget-core/d, Dojo 2 optionally supports the use of the jsx syntax known as tsx in TypeScript.

To start to use jsx in your project, widgets need to be named with a .tsx extension and some configuration is required in the project's tsconfig.json:

Add the configuration options for jsx:

"jsx": "react",
"jsxFactory": "tsx",

Include .tsx files in the project:

 "include": [
     "./src/**/*.ts",
     "./src/**/*.tsx"
 ]

Once the project is configured, tsx can be used in a widget's render function simply by importing the tsx function as:

import { tsx } from '@dojo/widget-core/tsx';

class MyWidgetWithTsx extends Themed(WidgetBase)<MyProperties> {
    protected render(): DNode {
        const { clear, properties: { completed, count, activeCount, activeFilter } } = this;

        return (
            <footer classes={this.theme(css.footer)}>
                <span classes={this.theme(css.count)}>
                    <strong>{`${activeCount}`}</strong>
                    <span>{`${count}`}</span>
                </span>
                <TodoFilter activeFilter={activeFilter} />
                { completed ? ( <button onclick={clear} /> ) : ( null ) }
            </footer>
        );
    }
}

Note: Unfortunately tsx is not directly used within the module so the tsx module will report as an unused import, and will need to be ignored by linters..

Web Components

Widgets can be turned into Custom Elements with minimal extra effort.

The customElement decorator can be used to annotate the widget class that should be converted to a custom element,

interface MyWidgetProperties {
	onClick: (event: Event) => void;
	foo: string;
	bar: string;
}

@customElement<MyWidgetProperties>({
	tag: 'my-widget',
	attribute: [ 'foo', 'bar' ],
	events: [ 'onClick' ]
})
class MyWidget extends WidgetBase<MyWidgetProperties> {
// ...
}

No additional steps are required. The custom element can be used in your application automatically. The decorator can be provided with configuration options to modify the functionality of the custom element.

Attributes

An array of attribute names that should be set as properties on the widget. The attribute name should be the same as the corresponding property on the widget.

Properties

An array of property names that will be accessible programmatically on the custom element but not as attributes. The property name must match the corresponding widget property.

Events

Some widgets have function properties, like events, that need to be exposed to your element. You can use the events array to specify widget properties to map to DOM events.

{
    events: [ 'onChange' ]
}

This will add a property to onChange that will emit the change custom event. You can listen like any other DOM event,

textWidget.addEventListener('change', function (event) {
    // do something
});

The name of the event is determined by removing the 'on' prefix from the name and lowercasing the resulting name.

Tag Name

Your widget will be registered with the browser using the provided tag name. The tag name must have a - in it.

Initialization

Custom logic can be performed after properties/attributes have been defined but before the projector is created. This allows you full control over your widget, allowing you to add custom properties, event handlers, work with child nodes, etc. The initialization function is run from the context of the HTML element.

{
    initialization(properties) {
        const footer = this.getElementsByTagName('footer');
        if (footer) {
            properties.footer = footer;
        }

        const header = this.getElementsByTagName('header');
        if (header) {
            properties.header = header;
        }
    }
}

It should be noted that children nodes are removed from the DOM when attached, and added as children to the widget instance.

How Do I Contribute?

We appreciate your interest! Please see the Dojo Meta Repository for the Contributing Guidelines.

Code Style

This repository uses prettier for code styling rules and formatting. A pre-commit hook is installed automatically and configured to run prettier against all staged files as per the configuration in the projects package.json.

An additional npm script to run prettier (with write set to true) against all src and test project files is available by running:

npm run prettier

Setup Installation

To start working with this package, clone the repository and run npm install.

In order to build the project, run grunt dev or grunt dist.

Testing

Test cases MUST be written using Intern using the Object test interface and Assert assertion interface.

90% branch coverage MUST be provided for all code submitted to this repository, as reported by Istanbul’s combined coverage results for all supported platforms.

To test locally in node run:

grunt test

To test against browsers with a local selenium server run:

grunt test:local

To test against BrowserStack or Sauce Labs run:

grunt test:browserstack

grunt test:saucelabs

Benchmarks

To run the JavaScript benchmarks, run:

npm run benchmark

The benchmarking setup relies heavily on js-framework-benchmark from GitHub.

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