How to Fix "Property 'checked' does not exist on type 'EventTarget'" TypeScript Error?

Why Does This Happen?

The checked property exists on the HTMLInputElement interface and not on the EventTarget object (which is the default type for an event target). This means that when you try to access the checked property on an event target, TypeScript will complain:

elem.addEventListener('click', function (e) {
  // Property 'checked' does not exist on type 'EventTarget'.
  console.log(e.target.checked);
}, false);

TypeScript complains in this instance because it cannot verify the existence of the checked property on the EventTarget type as this property is exclusively available on elements of type HTMLInputElement (specifically, when you use the <input type="radio"> or <input type="checkbox"> HTML element).

How to Fix the Issue?

To fix this issue, you can specify the correct type for the event target. Assuming that the event target is an HTML <input type="radio"> or <input type="checkbox"> element, you can fix this error in either of the following ways:

1. Using Type Assertion

   elem.addEventListener('click', (e) {
     // Property 'checked' does not exist on type 'EventTarget'.
     e.target.checked;
   
     // possible fix:
     (e.target as HTMLInputElement).checked;
   }, false);
   

2. Using Type Guard

   elem.addEventListener('click', (e) {
     // Property 'checked' does not exist on type 'EventTarget'.
     e.target.checked;
   
     // possible fix:
     if (e.target instanceof HTMLInputElement) {
       e.target.checked;
     }
   }, false);
   

   Using a type guard also provides type safety on runtime, where the target element can possibly be null or of a different type.

These solutions help TypeScript understand that the event target is indeed an HTMLInputElement, and it allows you to access the "checked" property without triggering a type error.

Further Reading

• How to Fix "Property '...' does not exist on type 'EventTarget'" TypeScript Error? (Designcise).