Single I/O Task Development (Promise and Async/Await)

Asynchronous concurrency provided by Promise and async/await is applicable to the development of a single I/O task. The following example uses the asynchronous concurrency capability to write data to a file.

1. Implement the logic of a single I/O task.

   import fs from '@ohos.file.fs';
   import { BusinessError } from '@ohos.base';
   import common from '@ohos.app.ability.common';
   
   async function write(data: string, file: fs.File): Promise<void> {
     fs.write(file.fd, data).then((writeLen: number) => {
       console.info('write data length is: ' + writeLen)
     }).catch((err: BusinessError) => {
       console.error(`Failed to write data. Code is ${err.code}, message is ${err.message}`);
     })
   }
   

2. Use the asynchronous concurrency capability to invoke the single I/O task. For details about how to obtain filePath in the example, see Obtaining Application File Paths.

   async function testFunc(): Promise<void>  {
     let context = getContext() as common.UIAbilityContext;
     let filePath: string = context.filesDir + "/test.txt"; // Application file path
     let file: fs.File = await fs.open(filePath, fs.OpenMode.READ_WRITE | fs.OpenMode.CREATE);
     write('Hello World!', file).then(() => {
       console.info('Succeeded in writing data.');
     }).catch((err: BusinessError) => {
       console.error(`Failed to write data. Code is ${err.code}, message is ${err.message}`);
     })
     fs.close(file);
   }
   testFunc();