if(typeof window === interface) ts code example

Example 1: typescript add global variable to window

declare global {
    interface Window {
        FB:any;
    }
}

let FB = window.FB; // ok now

Example 2: Property 'editor' does not exist on type 'Window & typeof globalThis'.

declare global {
    interface Window { MyNamespace: any; }
}

window.MyNamespace = window.MyNamespace || {};