异步/等待：理解异步/等待的问题

Question

我正在使用异步/等待。 我想先显示从可读流中检索到的数据，然后再显示相应的消息；

这是我的代码：

var stream = async function (){
           var myStream =  fs.createReadStream(__dirname+"/someText.txt",'utf8');

            await myStream.on('data', (chunk)=>{
             console.log(chunk)// I want to display this first
        }) 
 }

stream()

console.log('listening') // and then move on to display this one 

Answer 1

流监听器不是承诺，你不应该await myStream.on('data') 。 你可以这样做，但它会立即解决。

将流监听器包装在Promise中并等待它，为此您可以使用一次

const { once } = require('events');

var stream = async function (){
   var myStream =  fs.createReadStream(__dirname+"/someText.txt",'utf8');

    myStream.on('data', (chunk) => {
       console.log(chunk)// I want to display this first
    });

    // Wait until everything has been read
    // Or an error has been triggered
    await once(myStream, 'close'); 
}

(async() => {
  await stream(); // await can only be used in `async` function
  console.log('listening');
})().catch(console.error);