JSON Formatter, Minifier, and Validator in JavaScript / Node.js — Code Examples

JSON parsing and serialisation is built into every major language. Here is how to parse a JSON string, format (pretty-print) JSON, and handle common edge cases in each language.

JavaScript has JSON.parse() and JSON.stringify() built in. Use the space parameter of JSON.stringify() for pretty-printing.

// Parse JSON string → object
const obj = JSON.parse('{"name":"Alice","age":30}');
console.log(obj.name); // Alice

// Serialize object → JSON string
const json = JSON.stringify(obj);
console.log(json); // {"name":"Alice","age":30}

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

// Replacer function — exclude null values
const filtered = JSON.stringify(
  { a: 1, b: null, c: "hello" },
  (key, value) => (value === null ? undefined : value),
  2
);

// Reviver — parse dates automatically
const withDates = JSON.parse(
  '{"created":"2023-11-14T22:13:20Z"}',
  (key, value) =>
    typeof value === "string" && /^d{4}-d{2}-d{2}T/.test(value)
      ? new Date(value)
      : value
);
console.log(withDates.created instanceof Date); // true

• JSON.parse() throws SyntaxError on invalid JSON — wrap in try/catch.
• JSON.stringify() silently drops undefined values, functions, and Symbol keys.
• The replacer function in JSON.stringify() lets you control which keys are included.

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