The most common pattern to treat html as string is to use a a template language that works by replacing some patterns like {$variable} in the html with real data from a database.

A better way is to use html as what it really is, a dom document and with a simple glue language fill it with data, in this way you keep the html code unchanged for better maintainability and reuse.

For example a very basic way is to use a list of css selectors with the data that you want to fill eg:

div#id > span.class a = "lorem ipsum"

#product > .product-title = $product.title

Something like https://github.com/givanz/vtpl