List all class methods in Javascript

Question

The best way to explain my problem is through the below code:

class SomeClass {
  SomeMethod() {
    console.log("SomeMethod was called");
  }
}

var someInstance = new SomeClass();

// The below expression expected to return True but is returns False
console.log(
  someInstance.hasOwnProperty("SomeMethod")
);

// The below expression is expected to include SomeMethod in the return list, but it doesn't
console.log(
  Object.keys(someInstance)
);

// The below expression is expected to include SomeMethod in the return list, but it doesn't
console.log(
  Object.getOwnPropertyNames(someInstance)
);

// The below expression works fine which confrms that the function exists.
someInstance.SomeMethod();

CodeSandbox link

I would expect Object.keys() or Object.getOwnPropertyNames() to return all properties including methods defined in the class definition of the class from which this object was constructed but for some reason neither does.

If neither of these functions works in such a scenario then how can I list all methods of a class instance?

It might be instructive to take a look at the transpiled code for a class definition. — Dave Newton, Jul 04 '22 at 14:18
The method is called `.get**Own**PropertyNames()` for a reason: it does **not** return properties from the prototype chain. — Pointy, Jul 04 '22 at 14:20

score 1 · Accepted Answer · answered Jul 04 '22 at 14:26

You Can create custom function to acheive this

class SomeClass {
  SomeMethod() {
    console.log("SomeMethod was called");
  }
}

var someInstance = new SomeClass();
function getMethods(obj) {
  return Object.getOwnPropertyNames(Object.getPrototypeOf(obj))
    .filter(m => 'function' === typeof obj[m])
}
console.log(getMethods(someInstance))

List all class methods in Javascript

1 Answers1