JSON Handling

Parse and stringify JSON data.

2 min read | Node.js Tutorial

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JSON Handling

JSON (JavaScript Object Notation) is the standard for data exchange on the web. Node.js has built-in support for parsing and generating JSON.

Parsing JSON

const jsonString = '{"name": "Alice", "age": 30}';

// Parse JSON string to object
const user = JSON.parse(jsonString);
console.log(user.name);  // Alice

// Safe parsing with error handling
try {
  const data = JSON.parse(input);
} catch (err) {
  console.error("Invalid JSON:", err.message);
}

Stringifying JSON

const user = { name: "Alice", age: 30 };

// Convert object to JSON string
const json = JSON.stringify(user);
// '{"name":"Alice","age":30}'

// Pretty print with indentation
const pretty = JSON.stringify(user, null, 2);
// {
//   "name": "Alice",
//   "age": 30
// }

Reading and Writing JSON Files

const fs = require("fs").promises;

// Read JSON file
async function readJSON(filename) {
  const data = await fs.readFile(filename, "utf-8");
  return JSON.parse(data);
}

// Write JSON file
async function writeJSON(filename, data) {
  await fs.writeFile(filename, JSON.stringify(data, null, 2));
}

Replacer and Reviver

// Replacer: filter/transform during stringify
const filtered = JSON.stringify(user, (key, value) => {
  if (key === "password") return undefined;  // Exclude
  return value;
});

// Reviver: transform during parse
const parsed = JSON.parse(jsonString, (key, value) => {
  if (key === "date") return new Date(value);
  return value;
});