# Page Routing

> **NOTE**
>
> - The initial APIs of this module are supported since API version 8. Newly added APIs will be marked with a superscript to indicate their earliest API version.
> - Page routing APIs can be invoked only after page rendering is complete. Do not call the APIs in **onInit** and **onReady** when the page is still in the rendering phase.

## Modules to Import

```
import router from '@ohos.router'
```

## Required Permissions

None.

## router.push

push(options: RouterOptions): void

Navigates to a specified page in the application.

**System capability**: SystemCapability.ArkUI.ArkUI.Full

**Parameters**
| Name| Type| Mandatory| Description|
| -------- | -------- | -------- | -------- |
| options | [RouterOptions](#routeroptions) | Yes| Page routing parameters.|


**Example**
  ```js
  // Current page
  export default {
    pushPage() {
      router.push({
        url: 'pages/routerpage2/routerpage2',
        params: {
  	data1: 'message',
          data2: {
            data3: [123, 456, 789]
  	},
        },
      });
    }
  }
  ```
  ```js
  // routerpage2 page
  export default {
    data: {
      data1: 'default',
      data2: {
        data3: [1, 2, 3]
      }
    },
    onInit() {
      console.info('showData1:' + this.data1);
      console.info('showData3:' + this.data2.data3);
    }
  }
  ```


## router.replace

replace(options: RouterOptions): void

Replaces the current page with another one in the application and destroys the current page.

**System capability**: SystemCapability.ArkUI.ArkUI.Full

**Parameters**
| Name| Type| Mandatory| Description|
| -------- | -------- | -------- | -------- |
| options | [RouterOptions](#routeroptions) | Yes| Description of the new page.|

**Example**

  ```js
  // Current page
  export default {
    replacePage() {
      router.replace({
        url: 'pages/detail/detail',
        params: {
          data1: 'message',
        },
      });
    }
  }
  ```

  ```js
  // detail page
  export default {
    data: {
      data1: 'default'
    },
    onInit() {
      console.info('showData1:' + this.data1)
    }
  }
  ```

## router.back

back(options?: RouterOptions ): void

Returns to the previous page or a specified page.

**System capability**: SystemCapability.ArkUI.ArkUI.Full

**Parameters**
| Name| Type| Mandatory| Description|
| -------- | -------- | -------- | -------- |
| options | [RouterOptions](#routeroptions) | Yes| Description of the page. The **url** parameter indicates the URL of the page to return to. If the specified page does not exist in the page stack, the application does not respond. If this parameter is not set, the application returns to the previous page.|

**Example**
  ```js
  // index page
  export default {    
    indexPushPage() {        
      router.push({            
        url: 'pages/detail/detail',        
      });        
    }
  }
  ```

  ```js
  // detail page
  export default {    
    detailPushPage() {        
      router.push({            
        url: 'pages/mall/mall',        
      });    
    }
  }
  ```

  ```js
  // Navigate from the mall page to the detail page through router.back().
  export default {    
    mallBackPage() {        
      router.back();    
    }
  }
  ```

  ```js
  // Navigate from the detail page to the index page through router.back().
  export default {    
    defaultBack() {        
      router.back();    
    }
  }
  ```

  ```js
  // Return to the detail page through router.back().
  export default {    
    backToDetail() {        
      router.back({uri:'pages/detail/detail'});    
    }
  }
  ```

## router.clear

clear(): void

Clears all historical pages in the stack and retains only the current page at the top of the stack.

**System capability**: SystemCapability.ArkUI.ArkUI.Full

**Example**
  ```js
  export default {    
    clearPage() {        
      router.clear();    
    }
  }js
  ```

## router.getLength

getLength(): string

Obtains the number of pages in the current stack.

**System capability**: SystemCapability.ArkUI.ArkUI.Full

**Return value**
| Type| Description|
| -------- | -------- |
| string | Number of pages in the stack. The maximum value is **32**.|

**Example**
  ```js
  export default {     
    getLength() {        
      var size = router.getLength();        
      console.log('pages stack size = ' + size);    
    }
  }
  ```

## router.getState

getState(): RouterState

Obtains state information about the current page.

**System capability**: SystemCapability.ArkUI.ArkUI.Full

**Return value**

| Type                       | Description          |
| --------------------------- | -------------- |
| [RouterState](#routerstate) | Page routing state.|
## RouterState
Describes the page routing state.

**System capability**: SystemCapability.ArkUI.ArkUI.Full

| Name| Type| Description|
| -------- | -------- | -------- |
| index | number | Index of the current page in the stack.<br>>&nbsp;![icon-note.gif](public_sys-resources/icon-note.gif)&nbsp;**NOTE**<br>>&nbsp;The index starts from 1 from the bottom to the top of the stack.|
| name | string | Name of the current page, that is, the file name.|
| path | string | Path of the current page.|

**Example**
  ```js
  export default {     
    getState() {        
      var page = router.getState();
      console.log('current index = ' + page.index);
      console.log('current name = ' + page.name);
      console.log('current path = ' + page.path);
    }
  }
  ```

## router.enableAlertBeforeBackPage

enableAlertBeforeBackPage(options: EnableAlertOptions): void

Enables the display of a confirm dialog box before returning to the previous page.

**System capability**: SystemCapability.ArkUI.ArkUI.Full

**Parameters**
| Name| Type| Mandatory| Description|
| -------- | -------- | -------- | -------- |
| options | [EnableAlertOptions](#enablealertoptions) | Yes| Description of the dialog box.|

**Example**

  ```js
  export default {    
    enableAlertBeforeBackPage() {        
      router.enableAlertBeforeBackPage({            
        message: 'Message Info',            
        success: function() {                
          console.log('success');            
        },            
        fail: function() {                
          console.log('fail');            
        },        
      });    
    }
  }
  ```
## EnableAlertOptions

Describes the confirm dialog box.

**System capability**: SystemCapability.ArkUI.ArkUI.Full

| Name| Type| Mandatory| Description|
| -------- | -------- | -------- | -------- |
| message | string | Yes| Content displayed in the confirm dialog box.|

## router.disableAlertBeforeBackPage

disableAlertBeforeBackPage(): void

Disables the display of a confirm dialog box before returning to the previous page.

**System capability**: SystemCapability.ArkUI.ArkUI.Full

**Example**
  ```js
  export default {    
    disableAlertBeforeBackPage() {        
      router.disableAlertBeforeBackPage();    
    }
  }
  ```

##  router.getParams

getParams(): Object

Obtains the parameters passed from the page that initiates redirection to the current page.

**System capability**: SystemCapability.ArkUI.ArkUI.Full

**Return value**

| Type  | Description                              |
| ------ | ---------------------------------- |
| Object | Parameters passed from the page that initiates redirection to the current page.|

**Example**

- Web-like example
  ```js
  // Current page
  export default {
    pushPage() {
      router.push({
        url: 'pages/detail/detail',
        params: {
          data1: 'message',
        },
      });
    }
  }
  ```
  ```js
  // detail page
  export default {
    onInit() {
      console.info('showData1:' + router.getParams().data1);
    }
  }
  ```

- Declarative example

  ```ts
  // Navigate to the target page through router.push with the params parameter carried.
  import router from '@ohos.router'
  
  @Entry
  @Component
  struct Index {
    async  routePage() {
      let options = {
        url: 'pages/second',
        params: {
          text: 'This is the value on the first page.',
          data: {
            array: [12, 45, 78]
          },
        }
      }
      try {
        await router.push(options)
      } catch (err) {
        console.info(` fail callback, code: ${err.code}, msg: ${err.msg}`)
      }
    }
  
    build() {
      Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
          Text('This is the first page.')
            .fontSize(50)
            .fontWeight(FontWeight.Bold)
        Button() {
          Text('next page')
            .fontSize(25)
            .fontWeight(FontWeight.Bold)
        }.type(ButtonType.Capsule)
            .margin({ top: 20 })
            .backgroundColor('#ccc')
            .onClick(() => {
              this.routePage()
        })
      }
      .width('100%')
      .height('100%')
    }
  }
  ```

  ```ts
  // Receive the transferred parameters on the second page.
  import router from '@ohos.router'
  
  @Entry
  @Component
  struct Second {
    private content: string = "This is the second page."
    @State text: string = router.getParams()['text']
    @State data: any = router.getParams()['data']
    @State secondData : string = ''
    
    build() {
      Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
        Text(`${this.content}`)
          .fontSize(50)
          .fontWeight(FontWeight.Bold)
        Text(this.text)
          .fontSize(30)
          .onClick(()=>{
            this.secondData = (this.data.array[1]).toString()
          })
        .margin({top:20})
        Text('Value from the first page '+'' + this.secondData)
          .fontSize(20)
          .margin({top:20})
          .backgroundColor('red')      
      }
      .width('100%')
      .height('100%')
    }
  }
  ```

## RouterOptions

Describes the page routing options.

**System capability**: SystemCapability.ArkUI.ArkUI.Lite

| Name| Type| Mandatory| Description|
| -------- | -------- | -------- | -------- |
| url | string | Yes| URI of the destination page, in either of the following formats:<br>-&nbsp; Absolute path of the page. The value is available in the pages list in the config.json file, for example:<br>&nbsp;&nbsp;-&nbsp;pages/index/index<br>&nbsp;&nbsp;-&nbsp;pages/detail/detail<br>-&nbsp; Particular path. If the URI is a slash (/), the home page is displayed.|
| params | Object | No| Data that needs to be passed to the destination page during redirection. After the destination page is displayed, it can use the passed data, for example, **this.data1** (**data1** is a key in **params**). If there is the same key (for example, **data1**) on the destination page, the passed **data1** value will replace the original value on the destination page.|


  > ![icon-note.gif](public_sys-resources/icon-note.gif) **NOTE**
  > The page routing stack supports a maximum of 32 pages.