Based on some user input fields on a webpage, a string primitive is created that contains some C-style escape sequences. E.G. n t etc.

What is the proper, safe, way of decoding such a string? In most other languages that I’ve used for text processing the string format function can be used for this task; not just replacing magic variables. While it would also be nice if I could pass a map/dictionary/key-value object to the format specification and have it replace those too, it’s possible to work backwards with .replace and manually replace the values.

I’d rather not also re-invent the wheel for https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Lexical_grammar#escape_sequences and ideally all the other supported string Character Escapes could also be decoded https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Regular_expressions/Character_escape

"use strict";
// oversimplified JS function example
function someButtonClicked() {
  var userInput = document.getElementsByName("TextBox")[0].value;
  var parsed = "";
  // userInput contains: ntLine Two, with a tabnLine Three
  // userInput contains: "\n\tLine Two, with a tab\nLine Three"

  // I want to do the equivalent of this C style code
  // char parsed[strlen(userInput)] ; snprintf(parsed, strlen(userInput), userInput)
  // NOW parsed = "ntLine Two, with a tabnLine Three"
  // Note the previously escaped characters decoded to real characters.

  // parsed must be set within the function context, not global context...
  // After much searching and trial and error, all I've found is eval :(
  // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/eval
  eval("parsed = `" + userInput + "`")
}

Surely, there has to be a better way than this? However my efforts to use a search engine are greatly hampered by the poorly named ‘unescape’ (Really decodeURIComponent) https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/unescape