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Backend question · Object-oriented programming › Classes, constructors & fields

What does this print?

class User {
  id = 1;
  greet() { return "hi"; }
}
const u = new User();
console.log(Object.hasOwn(u, "greet"), Object.hasOwn(u, "id"), typeof User);
false true function

It prints false true function. A class is a constructor function, so typeof User is "function". Methods like greet are put once on User.prototype and shared by every instance. Fields like id = 1 are created on each instance by the constructor, so they are own properties.

"true true function" is tempting, but greet is not copied onto each object. The instance finds it through the prototype chain.