如何使用异步/等待正确读取文件? [英] How to read file with async/await properly?

问题描述

我无法弄清楚 async/await 是如何工作的.我有点明白，但我不能让它工作.

I cannot figure out how async/await works. I slightly understand it but I can't make it work.

function loadMonoCounter() {
    fs.readFileSync("monolitic.txt", "binary", async function(err, data) {
       return await new Buffer( data);
  });
}

module.exports.read = function() {
  console.log(loadMonoCounter());
};

我知道，我可以使用 readFileSync，但是如果我这样做了，我知道我永远不会理解 async/await 并且我'只会把问题埋起来.

I know, I could use readFileSync, but if I do, I know I'll never understand async/await and I'll just bury the issue.

目标:调用loadMonoCounter()并返回文件内容.

Goal: Call loadMonoCounter() and return the content of a file.

每次调用 incrementMonoCounter() 时(每次加载页面)，该文件都会递增.该文件包含二进制缓冲区的转储，并存储在 SSD 上.

That file is incremented every time incrementMonoCounter() is called (every page load). The file contains the dump of a buffer in binary and is stored on a SSD.

无论我做什么，我都会在控制台中收到错误或 undefined.

No matter what I do, I get an error or undefined in the console.

推荐答案

要使用 await/async 您需要返回承诺的方法.如果没有像 promisify:

To use await/async you need methods that return promises. The core API functions don't do that without wrappers like promisify:

const fs = require('fs');
const util = require('util');

// Convert fs.readFile into Promise version of same    
const readFile = util.promisify(fs.readFile);

function getStuff() {
  return readFile('test');
}

// Can't use `await` outside of an async function so you need to chain
// with then()
getStuff().then(data => {
  console.log(data);
})

注意，readFileSync 不接受回调，它返回数据或抛出异常.你没有得到你想要的值，因为你提供的函数被忽略了，你没有捕获实际的返回值.

As a note, readFileSync does not take a callback, it returns the data or throws an exception. You're not getting the value you want because that function you supply is ignored and you're not capturing the actual return value.

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