format.js

const format = (strings, ...values) => {
  if (values.every(v => typeof v !== "function")) {
    return strings.reduce((acc, str, i) => values[i] === undefined ? acc + str : acc + str + values[i], "")
  }
  return obj => strings.reduce((acc, str, i) => values[i] === undefined ? acc + str :
    typeof values[i] === "function" ? acc + str + values[i](obj) : acc + str + values[i], "")
}