How to Read JSON File in Node.js: Simple Guide

In Node.js, you can read a JSON file using the fs module's readFileSync or readFile methods, then parse the content with JSON.parse(). Alternatively, you can use import with assert { type: 'json' } in modern Node.js versions for direct JSON import.

Syntax

To read a JSON file in Node.js, you typically use the fs module to read the file content as a string, then convert it to a JavaScript object using JSON.parse().

• fs.readFileSync(path, encoding): Reads file synchronously.
• fs.readFile(path, encoding, callback): Reads file asynchronously.
• JSON.parse(string): Converts JSON string to object.

javascript

const fs = require('fs');

// Synchronous read
const data = fs.readFileSync('file.json', 'utf-8');
const obj = JSON.parse(data);

// Asynchronous read
fs.readFile('file.json', 'utf-8', (err, data) => {
  if (err) throw err;
  const obj = JSON.parse(data);
  console.log(obj);
});

Example

This example shows how to read a JSON file named data.json asynchronously and log its content as a JavaScript object.

javascript

import { readFile } from 'fs/promises';

async function readJson() {
  try {
    const data = await readFile('data.json', 'utf-8');
    const obj = JSON.parse(data);
    console.log(obj);
  } catch (error) {
    console.error('Error reading JSON file:', error);
  }
}

readJson();

Output

{ "name": "Alice", "age": 30 }

Common Pitfalls

Common mistakes when reading JSON files in Node.js include:

• Forgetting to specify the encoding (like 'utf-8'), which causes the data to be a buffer, not a string.
• Not handling errors from file reading or JSON parsing, which can crash your program.
• Using synchronous reading in performance-critical or server environments, which blocks the event loop.

javascript

const fs = require('fs');

// Wrong: missing encoding, data is a buffer
const data = fs.readFileSync('file.json');
const obj = JSON.parse(data.toString()); // Fixed: convert buffer to string

// Right: specify encoding to get string
const dataCorrect = fs.readFileSync('file.json', 'utf-8');
const objCorrect = JSON.parse(dataCorrect);

Quick Reference

Tips for reading JSON files in Node.js:

• Use fs/promises with async/await for clean asynchronous code.
• Always specify 'utf-8' encoding to get a string.
• Wrap JSON.parse() in try-catch to handle invalid JSON.
• For small config files, synchronous reading is okay during startup.
• In Node.js 18+, you can import JSON files directly using import data from './file.json' assert { type: 'json' }.

Key Takeaways

Use the fs module to read JSON files and JSON.parse() to convert to objects.

Always specify 'utf-8' encoding to read file content as a string.

Prefer asynchronous reading with async/await for non-blocking code.

Handle errors from file reading and JSON parsing to avoid crashes.

In modern Node.js, you can import JSON files directly with import assertions.