template.js

'use strict';

function str(strings, ...values) {
  let str = "";

  values.forEach((val, i) => {
    str += strings[i];
    str += values[i];
  })

  // the last chunk of string
  str += strings[strings.length-1];
  return str;
}

let apples = 3;
let oranges = 5;

// Sum of 3 + 5 = 8!
alert( str`Sum of ${apples} + ${oranges} = ${apples + oranges}!`);