react-proxy/src/deleteUnknownAutoBindMethods.js

function shouldDeleteClassicInstanceMethod(component, name) {
  if (component.__reactAutoBindMap.hasOwnProperty(name)) {
    // It's a known autobound function, keep it
    return false;
  }

  if (component[name].__reactBoundArguments !== null) {
    // It's a function bound to specific args, keep it
    return false;
  }

  // It's a cached bound method for a function
  // that was deleted by user, so we delete it from component.
  return true;
}

function shouldDeleteModernInstanceMethod(component, name) {
  const { prototype } = component.constructor;
  const prototypeDescriptor = Object.getOwnPropertyDescriptor(prototype, name);

  if (!prototypeDescriptor || !prototypeDescriptor.get) {
    // This is definitely not an autobinding getter
    return false;
  }

  if (prototypeDescriptor.get().length !== component[name].length) {
    // The length doesn't match, bail out
    return false;
  }

  // This seems like a method bound using an autobinding getter on the prototype
  // Hopefully we won't run into too many false positives.
  return true;
}

function shouldDeleteInstanceMethod(component, name) {
  const descriptor = Object.getOwnPropertyDescriptor(component, name);
  if (typeof descriptor.value !== 'function') {
    // Not a function, or something fancy: bail out
    return;
  }

  if (component.__reactAutoBindMap) {
    // Classic
    return shouldDeleteClassicInstanceMethod(component, name);
  } else {
    // Modern
    return shouldDeleteModernInstanceMethod(component, name);
  }
}

/**
 * Deletes autobound methods from the instance.
 *
 * For classic React classes, we only delete the methods that no longer exist in map.
 * This means the user actually deleted them in code.
 *
 * For modern classes, we delete methods that exist on prototype with the same length,
 * and which have getters on prototype, but are normal values on the instance.
 * This is usually an indication that an autobinding decorator is being used,
 * and the getter will re-generate the memoized handler on next access.
 */
export default function deleteUnknownAutoBindMethods(component) {
  const names = Object.getOwnPropertyNames(component);

  names.forEach(name => {
    if (shouldDeleteInstanceMethod(component, name)) {
      delete component[name];
    }
  });
}