How to read files asynchronously in node js, here is a simple function.
There are a lot of convoluted answers on the internet, does anyone agree if this is the simplest?
export default async function handler(req, res) {
let data = await readFiles('data/companies/');
res.status(200).json(data);
}
// async file reader
function readFiles(dirname) {
return new Promise(function (resolve, reject) {
let data = {}
fs.readdir(dirname, async function(err, filenames) {
filenames.forEach(function(filename) {
fs.readFile(dirname + filename, 'utf-8', function(err, content) {
if (err) {
reject(err)
}
data[filename] = content;
if (filenames.length === Object.keys(data).length) {
resolve(data)
}
});
});
});
})
}
A bit cleaner and easier using the built in promise support in fs.promises:
const fs = require('fs');
const fsp = fs.promises;
const path = require('path');
// async file reader
async function readFiles(dirname) {
const data = {};
const files = await fsp.readdir(dirname);
for (const filename of files) {
const full = path.join(dirname, filename);
const content = await fsp.readFile(full, {encoding: 'utf8'});
data[filename] = content;
}
return data;
}
Or, if you want to run your file operations in parallel (at least to the limit of the thread pool), you might get slightly faster end-to-end performance like this:
// async file reader
async function readFiles(dirname) {
const data = {};
const files = await fsp.readdir(dirname);
await Promise.all(files.map(async filename => {
const full = path.join(dirname, filename);
const content = await fsp.readFile(full, {encoding: 'utf8'});
data[filename] = content;
}));
return data;
}
Also, this:
res.status(200).json(data);
can be replaced with:
res.json(data);
200 is already the default status so there is no reason to specify it.