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):

JS
const fs = require('fs');
fs.readFile('/Users/joe/test.txt', 'utf8', (err, data) => {
if (err) {
console.error(err);
return;
}
console.log(data);
});

Alternatively, you can use the synchronous version fs.readFileSync():

JS
const fs = require('fs');
try {
const data = fs.readFileSync('/Users/joe/test.txt', 'utf8');
console.log(data);
} catch (err) {
console.error(err);
}

You can also use the promise-based fsPromises.readFile() method offered by the fs/promises module:

JS
const fs = require('fs/promises');
async function example() {
try {
const data = await fs.readFile('/Users/joe/test.txt', { encoding: 'utf8' });
console.log(data);
} catch (err) {
console.log(err);
}
}
example();

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.

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