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 '@ohos.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
Name 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();
        }
      },
    };
    

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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!',
  },
}

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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">parent component click</text>
  <text class="text-style" if="{{showValue}}">hello parent component!</text>
  <childComp id = "selfDefineChild"></childComp>
</div>
// parent.js
export default {
  data: {
    showValue: false,
    text: 'I am parent component!',
  },
  parentClicked () {
    this.showValue = !this.showValue;
    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}');
  },
}

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