JavaScript: get all method names of the provided object

getAllClassMethods.js

const getAllClassMethods = (obj) => {
  let keys = []
  let topObject = obj

  const onlyOriginalMethods = (p, i, arr) =>
    typeof topObject[p] === 'function' &&  // only the methods
    p !== 'constructor' && // not the constructor
    (i === 0 || p !== arr[i - 1]) && // not overriding in this prototype
    keys.indexOf(p) === -1 // not overridden in a child

  do {
    const l = Object.getOwnPropertyNames(obj)
      .sort()
      .filter(onlyOriginalMethods)
    keys = keys.concat(l)

    // walk-up the prototype chain
    obj = Object.getPrototypeOf(obj)
  } while (
    // not the the Object prototype methods (hasOwnProperty, etc...)
    obj && Object.getPrototypeOf(obj)
  )

  return keys
}