HarmonyOS 如何检测webview滚动是否触底

import web_webview from '@ohos.web.webview'; 
 
@Entry 
@Component 
struct WebPage { 
  controller: web_webview.WebviewController = new web_webview.WebviewController() 
 
  build() { 
    Column() { 
      Web({ src: $rawfile('123.pdf'), controller: this.controller }) 
        .javaScriptAccess(true) 
        .domStorageAccess(true) 
        .verticalScrollBarAccess(true) 
        .onOverScroll((event) => { 
          if (event.yOffset < 0) { 
            console.log('已到达顶端') 
          } 
          if (event.yOffset > 0) { 
            console.log('已到达底端') 
          } 
        }) 
    } 
  } 
}