Pretty-print a JSON object with JavaScript

Pretty-printing refers to the process of making some data more human-readable. In regards to JSON, it's primarily the process of indenting the data so that it is easier to read. This is pretty easy to accomplish, using JSON.stringify() with the appropriate arguments.

const obj = {
  id: 1182,
  username: 'johnsmith',
  active: true,
  emails: ['johnsmith@mysite.com', 'contact@johnsmi.th'],
};

JSON.stringify(obj, null, 2);
// {
//   "id": 1182,
//   "username": "johnsmith",
//   "active": true,
//   "emails": [
//     "johnsmith@mysite.com"
//     "contact@johnsmi.th"
//   ]
// }

As you can see in this example, the third argument of JSON.stringify() is the number of spaces to indent each level of the object. Additionally, you can use the second argument to specify a replacer function. This can come in handy if you want to provide custom formatting for certain types of values or specific key-value pairs.

const obj = {
  id: 1182,
  username: 'johnsmith',
  active: true,
  emails: ['johnsmith@mysite.com', 'contact@johnsmi.th'],
};

const replacer = (key, value) => {
  if (key === 'id') return value.toString(16);
  if (key === 'username') return `@${value}`;
  if (key === 'emails') return `${value[0]} +${value.length - 1} more`;
  return value;
};

JSON.stringify(obj, replacer, 2);
// {
//   "id": "0x4e2",
//   "username": "@johnsmith",
//   "active": true,
//   "emails": "johnsmith@mysite.com +1 more"
// }