Using .map() to mutate object properties

map-mutate.js

const objects = [
  {id: 10, name: "Doe", firstname: "John", slug: "john"},
  {id: 20, name: "Doe", firstname: "Jane", slug: "jane"},
  {id: 30, name: "Mitchell", firstname: "John", slug: "john"},
  {id: 40, name: "Money", firstname: "Boy", slug: "boy"}
];

const result = objects.map(obj => {
  obj.slug = `${obj.firstname}-${obj.name}`.toLowerCase()
  return obj;
});