New Typescript 1.8.4 build error: ” Build: Property ‘result’ does not exist on type ‘EventTarget’. “

Instead of using event.target.result, you can just use FileReader.result.

For example,

const fileReader: FileReader = new FileReader();

fileReader.onload = (event: Event) => {
   event.target.result; // This is invalid
   fileReader.result; // This is valid
};