JSON Processing in Node.js: A Complete Guide

JSON processing in Node.js: a complete guide

JSON (JavaScript Object Notation) is a lightweight data interchange format based on JavaScript object syntax. In the Node.js environment, working with JSON is a daily task: from configuration files to API requests. In this article, we will cover all aspects of JSON processing in detail, including parsing, serialization, validation, and working with large files.

Basic methods: JSON.parse() and JSON.stringify()

Two main methods for working with JSON are built directly into JavaScript. They are globally available and do not require installing additional libraries.

JSON.parse() — converting a string to an object

The JSON.parse() method takes a JSON string and returns the corresponding JavaScript object. If the string contains invalid JSON, a SyntaxError exception will be thrown.

const jsonString = '{"name": "Anna", "age": 28, "isStudent": false}';const user = JSON.parse(jsonString);console.log(user.name); // "Anna"console.log(user.age);  // 28

An optional second parameter can be a reviver function that allows modifying values during parsing:

const json = '{"year": "2024", "price": "1500.50"}';const data = JSON.parse(json, (key, value) => {  if (key === 'price') return parseFloat(value);  if (key === 'year') return parseInt(value);  return value;});console.log(typeof data.price); // "number"

JSON.stringify() — converting an object to a string

The JSON.stringify() method does the opposite: it converts an object or value into a JSON string. It accepts up to three arguments: the value, a replacer function or array of keys, and the number of spaces for formatting.

const user = {  name: "Ivan",  age: 32,  skills: ["JS", "Node", "Python"]};

// Without formattingconsole.log(JSON.stringify(user));// {"name":"Ivan","age":32,"skills":["JS","Node","Python"]}

// With formatting (2 spaces)console.log(JSON.stringify(user, null, 2));/*{  "name": "Ivan",  "age": 32,  "skills": [    "JS",    "Node",    "Python"  ]}*/

The second argument can be an array of keys for filtering:

console.log(JSON.stringify(user, ['name', 'age']));// {"name":"Ivan","age":32}

Working with JSON files in Node.js

In Node.js, it is often necessary to read and write JSON files. The fs (file system) modules are used for this.

Reading a JSON file

const fs = require('fs');

// Synchronous readingtry {  const data = fs.readFileSync('config.json', 'utf8');  const config = JSON.parse(data);  console.log(config.port);} catch (err) {  console.error('File reading error:', err.message);}

// Asynchronous readingfs.readFile('config.json', 'utf8', (err, data) => {  if (err) {    console.error('Error:', err);    return;  }  const config = JSON.parse(data);  console.log(config.port);});

Writing a JSON file

const fs = require('fs');

const settings = {  theme: 'dark',  language: 'en',  fontSize: 14};

// Synchronous writingfs.writeFileSync('settings.json', JSON.stringify(settings, null, 2));

// Asynchronous writingfs.writeFile('settings.json', JSON.stringify(settings, null, 2), (err) => {  if (err) console.error('Write error:', err);  else console.log('File saved');});

JSON validation

Before using data, it is always worth checking its validity. The simplest way is to wrap JSON.parse() in a try-catch. For more complex structure validation, libraries can be used.

Checking with try-catch

function safeJsonParse(str) {  try {    return { data: JSON.parse(str), error: null };  } catch (e) {    return { data: null, error: e.message };  }}