stringify-with-replacer-demo.js

const user = {
  id: 101010,
  name: "Derek",
  email: "[email protected]"
};
function replacer(key, value) {
  if (typeof value === "number") {
    return undefined;
  }
  if (key === "email") {
    return "Removed for privacy";
  }
  return value;
}
console.log(JSON.stringify(user));
// result: {"id":101010,"name":"Derek","email":"[email protected]"} 
console.log(JSON.stringify(user, replacer));
// result: {"name":"Derek","email":"Removed for privacy"} 
console.log(JSON.stringify(user, null, "^_^ "));
// result: {
// ^_^ "id": 101010,
// ^_^ "name": "Derek",
// ^_^ "email": "[email protected]"
// }