Evaluating string interpolation for template literals

[73R3WY]

I encountered this issue while trying out the string interpolation feature of ES6

the code is

...
    if (unevaluated_lines) {
        let num_lines_message = (`${unevaluated_lines} answer ${unevaluated_lines == 1 ? "line was" : "lines were"} not evaluated.`)
        submit.reject(Error("Please give an evaluation to every answer line. " + num_lines_message))
...

but the saved string in the variable num_lines_message does follow spacing between string literals but the line of code unassigned to a variable works fine. See screenshot below:

Using Google Chrome: