TypeScript - Pattern for passing object to function & setting defaults

I'm fairly new to TS and wanted some advice on how to pass an object literal to a method in the most efficient manner.

E.g. (called in html)

<script>
    app.setOptions({
        width: 820,
        height: 450,
        bgColor: '#fff'
    });
</script>

In main.ts

module app {

    app.setOptions = function(options: { width: number, height: number, bgColor: string}) {
        options.width   = options.width || 600,
        options.height  = options.height || 300,
        options.bgColor = options.bgColor || '#fff';

        initializeApp(options);
    }
}

Note: This works fine, although I'm warned about 'the property setOptions does not exist on type 'typeof app'. I'm going to add loads more options too.