JSON.parse() Complete Guide: Reviver Function, Error Handling, and Edge Cases

What is JSON.parse()?

JSON.parse() parses a JSON string and returns the corresponding JavaScript value. It is the standard way to deserialize JSON from APIs, files, and storage.

Basic Usage

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

Always Wrap in Try/Catch

JSON.parse() throws a SyntaxError on invalid input. Never call it without error handling in production code.

function safeJsonParse(str, fallback = null) {
  try {
    return JSON.parse(str);
  } catch {
    return fallback;
  }
}

// Usage
const data = safeJsonParse(responseText, {});

The Reviver Function

The optional second argument to JSON.parse() is called for every key/value pair and lets you transform values during parsing.

// Auto-revive ISO date strings to Date objects
const data = JSON.parse(json, (key, value) => {
  if (typeof value === 'string' && /^\d{4}-\d{2}-\d{2}T/.test(value)) {
    return new Date(value);
  }
  return value;
});

Common Errors and Fixes

Validate your JSON before parsing with the free JSON validator at jsondecode.com.