I cannot figure out how async
/await
works. I slightly understands 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());
};
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.
Goal: Call loadMonoCounter()
and return the content of a file.
That file is incremented every time incrementMonoCounter()
is called (every page load). The file contain the dump of a buffer in binary and is stored on a SSD.
No matter what I do, I get an error or undefined
in the console.
This question is related to
node.js
asynchronous
readfile
There is a fs.readFileSync( path, options )
method, which is synchronous.
You can easily wrap the readFile command with a promise like so:
async function readFile(path) {
return new Promise((resolve, reject) => {
fs.readFile(path, 'utf8', function (err, data) {
if (err) {
reject(err);
}
resolve(data);
});
});
}
then use:
await readFile("path/to/file");
To keep it succint and retain all functionality of fs
:
const fs = require('fs');
const fsPromises = fs.promises;
async function loadMonoCounter() {
const data = await fsPromises.readFile('monolitic.txt', 'binary');
return new Buffer(data);
}
Importing fs
and fs.promises
separately will give access to the entire fs
API while also keeping it more readable... So that something like the next example is easily accomplished.
// the 'next example'
fsPromises.access('monolitic.txt', fs.constants.R_OK | fs.constants.W_OK)
.then(() => console.log('can access'))
.catch(() => console.error('cannot access'));
This is TypeScript version of @Joel's answer. It is usable after Node 11.0:
import { promises as fs } from 'fs';
async function loadMonoCounter() {
const data = await fs.readFile('monolitic.txt', 'binary');
return Buffer.from(data);
}
You can use fs.promises
available natively since Node v11.0.0
import fs from 'fs';
const readFile = async filePath => {
try {
const data = await fs.promises.readFile(filePath, 'utf8')
return data
}
catch(err) {
console.log(err)
}
}
Since Node v11.0.0 fs promises are available natively without promisify
:
const fs = require('fs').promises;
async function loadMonoCounter() {
const data = await fs.readFile("monolitic.txt", "binary");
return new Buffer(data);
}
Source: Stackoverflow.com