NativeScript/apps/ui/app/bottom-navigation/icon-change-page.ts

import { BottomNavigation, SelectedIndexChangedEventData } from '@nativescript/core/ui/bottom-navigation';

export function onSelectedIndexChanged(args: SelectedIndexChangedEventData) {
	const bottomNav = <BottomNavigation>args.object;

	const newItem = bottomNav.tabStrip.items[args.newIndex];
	if (newItem) {
		newItem.iconSource = 'res://icon';
		newItem.title = 'selected';
	}

	const oldItem = bottomNav.tabStrip.items[args.oldIndex];
	if (oldItem) {
		oldItem.iconSource = 'res://testlogo';
		oldItem.title = 'unselected';
	}
}