Quirk - JSON.stringify removes empty properties

Problem

I noticed that when I was upserting docs in mongodb the fields where not getting reset because the value coming in was undefined instead of null.

Solution

Pass a custom replacer function to to JSON.stringify() so when a value is undefined, we use null instead.

const user = { name: 'Quirky', phone: undefined };

const replacer = (key, value) => (typeof value === 'undefined' ? null : value);

const stringified = JSON.stringify(user, replacer);
// -> "{\"name\":\"Quirky\",\"phone\":null}"