.update()

Updates the provided key's value with the provided callback.

update(key, updateCallback)

Parameter	Description
key	String The target key
updateCallback	Callback Function to call to update the data

Returns	Description
JSONData	The updated data from the provided key's root

db.set('user', { name: 'Peter' }); // { name: 'Peter' }

db.update('user', (d) => d.name += "👨🏻‍💻"); // { name: 'Peter👨🏻‍💻' }

Also allows the use of dot notation:

db.get('user'); // { name: '5antos' }

db.update('user.name', (d) => d = d.toUpperCase()); // { name: '5ANTOS' }

And even a way to delete a key from the data:

db.get('person'); // { name: 'Peter', age: 19 }

db.update('person', (d) => delete d.age); // { name: 'Peter' } 

When the callback parameter's value is not an object, the value that the update callback returns will be the value that will replace the old one, so it's optional to redefine its value inside the callback:

db.get('user'); // { name: '5ANTOS' }

db.update('user.name', (d) => d = d.toLowerCase()); // { name: '5antos' }
// is the same as
db.update('user.name', (d) => d.toLowerCase()); // { name: '5antos' }