JQuery: how to replace all between certain characters?

Question

I have searched for a general solution to this but only find answers to peoples specific questions.

Basically, I want to know how to generally use .replace() to repl

Answer 1

    String.prototype.replaceBetween = function(opentag, closetag, replacement) {
      var read_index = 0;
      var open_index = 0;
      var close_index = 0;
      var output = '';

      while ((open_index = this.indexOf(opentag, read_index)) != -1) {
        output += this.slice(read_index, open_index) + opentag;
        read_index = open_index + opentag.length;

        if ((close_index = this.indexOf(closetag, read_index)) != -1) {
          if (typeof replacement === 'function') {
            output += replacement(this.substring(open_index + opentag.length, close_index - 1)) + closetag;
          } else {
            output += replacement + closetag;
          }
          read_index = close_index + closetag.length;
        }
      }

      output += this.slice(read_index);

      return output
    };

    var mydiv = document.getElementById("mydiv");
    var html = mydiv.innerHTML;
    html = html.replaceBetween("", "", "hello");
    html = html.replaceBetween("", "", function(body) {
      return body + ' world';
    });
    mydiv.innerHTML = html;

The begining...for and bar... the end.