Type Assertion

handler.ts

// Problem
function handler(event: Event) {
    let element = event as HTMLElement; // Error : Neither 'Event' not type 'HTMLElement' is assignable to the other
}

// Approach 1 (using any)
function handler(event: Event) {
    let element = event as any as HTMLElement; // Basarat calls this "double assertion"
}

// Approach 2 (using union types)
function handler(eventOrElement: Event | HTMLElement) {
    let element = eventOrElement as HTMLElement;
}

// Source: https://basarat.gitbooks.io/typescript/content/docs/types/type-assertion.html