Simple String.format() in Javascript

String.prototype.format = function() {
  a = this;
  for (k in arguments) {
    a = a.replace("{" + k + "}", arguments[k])
  }
  return a
}

Usage:

console.log("Hello, {0}!".format("World"))

https://coderwall.com/p/flonoa/simple-string-format-in-javascript