Reading files with Node.js
The simplest way to read a file in Node.js is to use the fs.readFile() method, passing it the file path, encoding and a callback function that will be called with the file data (and the error):
const = ('node:fs');
.('/Users/joe/test.txt', 'utf8', (, ) => {
if () {
.();
return;
}
.();
});
Alternatively, you can use the synchronous version fs.readFileSync():
const = ('node:fs');
try {
const = .('/Users/joe/test.txt', 'utf8');
.();
} catch () {
.();
}
You can also use the promise-based fsPromises.readFile() method offered by the fs/promises module:
const = ('node:fs/promises');
async function () {
try {
const = await .('/Users/joe/test.txt', { : 'utf8' });
.();
} catch () {
.();
}
}
();
All three of fs.readFile(), fs.readFileSync() and fsPromises.readFile() read the full content of the file in memory before returning the data.
This means that big files are going to have a major impact on your memory consumption and speed of execution of the program.
In this case, a better option is to read the file content using streams.
import from 'fs';
import { } from 'node:stream/promises';
import from 'path';
const = 'https://www.gutenberg.org/files/2701/2701-0.txt';
const = .(.(), 'moby.md');
async function (, ) {
const = await ();
if (!. || !.) {
// consuming the response body is mandatory: https://undici.nodejs.org/#/?id=garbage-collection
await .?.();
throw new (`Failed to fetch ${}. Status: ${.}`);
}
const = .();
.(`Downloading file from ${} to ${}`);
await (., );
.('File downloaded successfully');
}
async function () {
const = .(, { : 'utf8' });
try {
for await (const of ) {
.('--- File chunk start ---');
.();
.('--- File chunk end ---');
}
.('Finished reading the file.');
} catch () {
.(`Error reading file: ${.message}`);
}
}
try {
await (, );
await ();
} catch () {
.(`Error: ${.message}`);
}