在onLoadIntercept和onPageBegin哪个方法中执行runJavaScript能保证既能注入成功，时机又尽量的靠前。

Web({ src: 'www.baidu.com', controller: this.webviewController }) 
  .onControllerAttached(() => { 
    try { 
      let defaultUA: string = this.webviewController.getUserAgent(); 
      console.info(`Invoke webviewController.getUserAgent/setCustomUserAgent succeed! customUA: ${defaultUA}`); 
      this.webviewController.setCustomUserAgent(`${defaultUA}customUA`); 
      const curUA: string = this.webviewController.getCustomUserAgent(); 
      console.info(`Invoke webviewController.getUserAgent/setCustomUserAgent succeed! err: ${curUA}`); 
    } catch (err) { 
      console.error(`Invoke webviewController.getUserAgent/setCustomUserAgent failed! err: ${JSON.stringify(err)}`); 
    } 
  })
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