> JS and JSX are isomorphic

They are not

Or, if they are, they are in the same way of a custom XML templating language that can be translated to a specific javascript library implementation and then back to XML

In the same way, is Mustache isomorphic?

    "{{title}} spends {{calc}}"

can be translated to

    `${title} spends ${calc}`

and back to

    "{{title}} spends {{calc}}"