How to nicely return HTML from function?

Ionic Framework ionic-v3
1

I’m using c3.js to build charts, it uses a function that returns HTML to create a tooltip,
currently my code is :

generateToolTip (param1: string, param2: string) : string {
	return "
		<div>
			<div>
				" + param1 + "
			</div>
			<div>
				" + param2 + "
			</div>
			...
		</div>
	";
}

Is there a way to properly generate this html from HTML template file?
Something like this :

generateToolTip (param1: string, param2: string) : string {
	return render('MyTemplate.html', param1, param2);
}

MyTemplate.html [
	
	<div>
		{{ param1 }}
	</div>
	<div>
		{{ param2 }}
	</div>
]