HarmonyOS如何在ts中调用ets文件中的变量

let context = getContext(this) as common.UIAbilityContext;  
export let filesDir = context.filesDir; 

async screenshot(): Promise<string> { 
  const timestamp = Date.now(); 
  // 这里需要依赖应用所在的沙箱目录。 
  const filename = filesDir + `/data/cache/screenshot_${timestamp}.png`; 
  try { 
  let status = await this.driver.screenCapture(filename); 
  if (status == true){ 
  // 这里读取截图拿到其对应的字节并返回 
  return imageData; 
} 
else 
throw new Error("screenCapture failed."); 
} catch (error) { 
  Logger.error(TAG, `screenshot failed:${error}`); 
  throw error; 
} 
}