Argument of type '(e: CustomEvent) => void' is not assignable to parameter of type 'EventListenerOrEventListenerObject'

Question

I have this custom event setup, and it works with TypeScript 2.5.3, but when I updated to 2.6.1 I get an error

window.addEventListener(         


        

Answer 1

I created a generic function based off @jcalz's answer

/**
 * Checks whether an object can be safely cast to its child type
 * @param parent the object to be 'narrowly' cast down to its child type
 * @param checkForProps props which aught to be present on the child type
 */
export function isSubTypeWithProps(parent: P, ...checkForProps: (keyof C)[]): parent is C {
  return checkForProps.every(prop => prop in parent);
}

/**
 * Usage example
 */
const el = document.getElementById('test');
el.addEventListener('click', (e: Event) => {
  if (isSubTypeWithProps(e, 'which')) {
    if (e.which === 1) { // primary mouse button only ('which' prop is only available on MouseEvent)
      console.log('clicked');
    }
  }
});