Angular 2 typescript invoke javascript function

You have to tell TypeScript about external (JavaScript) declarations using declare. See https://www.typescriptlang.org/docs/handbook/writing-declaration-files.html

interface MyTheme {
    documentOnLoad: Function;
    documentOnReady: Function;
}
declare var MYTHEME: MyTheme;

Or anonymously

declare var MYTHEME: {documentOnLoad: Function, documentOnReady: Function};