JavaScript

You can use a .js file in the ECMAScript compliant JavaScript language to define the service logic of an HML page. With dynamic typing, JavaScript can make your application more expressive with a flexible design. The following describes the JavaScript compilation and running.

Syntax

The ES6 syntax is supported.

• Module declaration

  Import functionality modules.

  import router from '@system.router';

• Code reference

  Import JavaScript code.

  import utils from '../../common/utils.js';

Objects

• Application objects

  Name	Type	Description
  $def	Object	Object that is exposed in the app.js file and obtained by this.$app.$def. > NOTE > Application objects do not support data binding. Data update should be triggered on the UI.

  Example

  // app.js
  export default {
    onCreate() {
      console.info('Application onCreate');
    },
    onDestroy() {
      console.info('Application onDestroy');
    },
    globalData: {
      appData: 'appData',
      appVersion: '2.0',
    },
    globalMethod() {
      console.info('This is a global method!');
      this.globalData.appVersion = '3.0';
    }
  };

  // index.js
  export default {
    data: {
      appData: 'localData',
      appVersion:'1.0',
    },
    onInit() {
      this.appData = this.$app.$def.globalData.appData;
      this.appVersion = this.$app.$def.globalData.appVersion;
    },
    invokeGlobalMethod() {
      this.$app.$def.globalMethod();
    },
    getAppVersion() {
      this.appVersion = this.$app.$def.globalData.appVersion;
    }
  }

• Page objects

  Attribute	Type	Description
  data	Object/Function	Data model of the page. If the attribute is of the function type, the return value must be of the object type. The attribute name cannot start with a dollar sign ($) or underscore (_). Do not use reserved words (for, if, show, and tid). Do not use this attribute and private or public at the same time.
  $refs	Object	DOM elements or child component instances that have registered the ref attribute. For example code, see Obtaining a DOM element.
  private	Object	Data model of the page. Private data attribute can be modified only on the current page.
  public	Object	Data model of the page. Behaviors of public data attributes are the same as those of the data attribute.
  props	Array/Object	Used for communication between components. This attribute can be transferred to components via <tag xxxx='value'>. A props name must be in lowercase and cannot start with a dollar sign ($) or underscore (_). Do not use reserved words (for, if, show, and tid). Currently, props does not support functions. For details, see props.
  computed	Object	Used for pre-processing an object for reading and setting. The result is cached. The name cannot start with a dollar sign ($) or underscore (_). Do not use reserved words. For details, see props.

Methods

• Data methods

  Name	Parameter	Description
  $set	key: string, value: any	Adds an attribute or modifies an existing attribute. Usage: this.$set('key',value): Add an attribute.
  $delete	key: string	Deletes an attribute. Usage: this.$delete('key'): Delete an attribute.

  Example

  // index.js
  export default {
    data: {
      keyMap: {
        OS: 'OpenHarmony',
        Version: '2.0',
      },
    },
    getAppVersion() {
      this.$set('keyMap.Version', '3.0');
      console.info("keyMap.Version = " + this.keyMap.Version); // keyMap.Version = 3.0
  
      this.$delete('keyMap');
      console.info("keyMap.Version = " + this.keyMap); // log print: keyMap.Version = undefined
    }
  }

• Public methods

  Name	Parameter	Description
  $element	id: string	Obtains the component with a specified ID. If no ID is specified, the root component is returned. For example code, see Obtaining a DOM element. Usage: <div id='_xxx_'></div> - this.$element('xxx'): Obtain the component whose ID is xxx. - this.$element(): Obtain the root component.
  $rootElement	None	Obtains the root element. Usage: this.$rootElement().scrollTo({ duration: 500, position: 300 }), which scrolls the page by 300 px within 500 ms.
  $root	N/A	Obtains the root ViewModel instance. For example code, see Obtaining the ViewModel.
  $parent	N/A	Obtains the parent ViewModel instance. For example code, see Obtaining the ViewModel.
  $child	id: string	Obtains the ViewModel instance of a custom child component with a specified ID. For example code, see Obtaining the ViewModel. Usage: this.$child('xxx'): Obtain the ViewModel instance of a custom child component whose ID is xxx.

• Event methods

  Name	Parameter	Description
  $watch	data: string, callback: string | Function	Listens for attribute changes. If the value of the data attribute changes, the bound event is triggered. For details, see props Usage: this.$watch('key', callback)

• Page methods

  Name	Parameter	Description
  scrollTo6+	scrollPageParam: ScrollPageParam	Scrolls the page to the target position. You can specify the position using the ID selector or scrolling distance.

  Table 1 ScrollPageParam⁶⁺

  Name	Type	Default Value	Description
  position	number	-	Position to scroll to.
  id	string	-	ID of the element to be scrolled to.
  duration	number	300	Scrolling duration, in milliseconds.
  timingFunction	string	ease	Animation curve for scrolling. Available options: Animation Styles
  complete	() => void	-	Callback to be invoked when the scrolling is complete.

  Example

  this.$rootElement().scrollTo({position: 0})
  this.$rootElement().scrollTo({id: 'id', duration: 200, timingFunction: 'ease-in', complete: ()=>void})

Obtaining a DOM Element

1. Use $refs to obtain a DOM element.

   <!-- index.hml -->
   <div class="container">
     <image-animator class="image-player" ref="animator" images="{{images}}" duration="1s" onclick="handleClick"></image-animator>
   </div>

   // index.js
   export default {
     data: {
       images: [
         { src: '/common/frame1.png' },
         { src: '/common/frame2.png' },
         { src: '/common/frame3.png' },
       ],
     },
     handleClick() {
       const animator = this.$refs.animator; // Obtain the DOM element whose $refs attribute is animator.
       const state = animator.getState();
       if (state === 'paused') {
         animator.resume();
       } else if (state === 'stopped') {
         animator.start();
       } else {
         animator.pause();
       }
     },
   };

2. Call $element to obtain a DOM element.

   <!-- index.hml -->
   <div class="container" style="width:500px;height: 700px; margin: 100px;">
     <image-animator class="image-player" id="animator" images="{{images}}" duration="1s" onclick="handleClick"></image-animator>
   </div>

   // index.js
   export default {
     data: {
       images: [
         { src: '/common/frame1.png' },
         { src: '/common/frame2.png' },
         { src: '/common/frame3.png' },
       ],
     },
     handleClick() {
       const animator = this.$element('animator'); // Obtain the DOM element whose ID is animator.
       const state = animator.getState();
       if (state === 'paused') {
         animator.resume();
       } else if (state === 'stopped') {
         animator.start();
       } else {
         animator.pause();
       }
     },
   };

Obtaining the ViewModel

The following shows files of the root page:

<!-- root.hml -->
<element name='parentComp' src='../../common/component/parent/parent.hml'></element>
<div class="container">
  <div class="container">
    <text>{{text}}</text>
    <parentComp></parentComp>
  </div>
</div>

// root.js
export default {
  data: {
    text: 'I am a root!',
  },
}

Customize the parent component.

<!-- parent.hml -->
<element name='childComp' src='../child/child.hml'></element>
<div class="item" onclick="textClicked">
  <text class="text-style" onclick="parentClicked">Click this parent component</text>
  <text class="text-style" if="{{show}}">Hello parent component!</text>
  <childComp id = "selfDefineChild"></childComp>
</div>

// parent.js
export default {
  data: {
    show: false,
    text: 'I am the parent component!',
  },
  parentClicked () {
    this.show = !this.show;
    console.info('parent component get parent text');
    console.info(`${this.$parent().text}`);
    console.info("The parent component gets the child function.");
    console.info(`${this.$child('selfDefineChild').childClicked()}`);
  },
}

Customize the child component.

<!-- child.hml -->
<div class="item" onclick="textClicked">
  <text class="text-style" onclick="childClicked">Child component clicked</text>
  <text class="text-style" if="{{isShow}}">Hello child component</text>
</div>

// child.js
export default {
  data: {
    isShow: false,
    text: 'I am the child component!',
  },
  childClicked () {
    this.isShow = !this.isShow;
    console.info('child component get parent text');
    console.info('${this.$parent().text}');
    console.info('child component get root text');
    console.info('${this.$root().text}');
  },
}