NativeScript/tests/app/pages/fonts-test.ts

import * as stack from "tns-core-modules/ui/layouts/stack-layout";
import { unsetValue } from "tns-core-modules/ui/core/view";

export function buttonTap(args) {
    var stackLayout = <stack.StackLayout>args.object.parent;

    for (var i = 0; i < stackLayout.getChildrenCount(); i++) {
        var v = stackLayout.getChildAt(i);
        v.style.fontFamily = unsetValue;
        v.style.fontSize = unsetValue;
        v.style.fontStyle = unsetValue;
        v.style.fontWeight = unsetValue;

        v.style.color = unsetValue;
        v.style.textAlignment = unsetValue;
    }
}