default values in javascript template strings

Question

Is there any way to access the javascript template-string engine to provide default values for undefined variables?

console.log(`this variable is undefined: ${x}`) 
// throws ReferenceError

// but i want to generate something like this:
"this variable is undefined: <warning! undefined variable>"

This would be ok, too:

function tag(strings,...values){
   // values[i] should be "undefined" if this variable is undefined
}
tag`${x}`

If thats not possible, is there a template string engine that does exactly what javascript does and has this feature?

Answer 1

You can use the || to coalasce the value, like:

console.log(`this variable is undefined: ${x || '<warning! undefined variable>'}`)