A very simple jQuery based textarea editor

simple_editor.js

// This is shamelessly copied from http://stackoverflow.com/questions/263743/how-to-get-cursor-position-in-textarea#answer-3373056
function getInputSelection(el) {
  var start = 0, end = 0, normalizedValue, range, textInputRange, len, endRange;
  if (typeof el.selectionStart == "number" && typeof el.selectionEnd == "number") {
    start = el.selectionStart;
    end = el.selectionEnd;
  }
  else {
    range = document.selection.createRange();
    if (range && range.parentElement() == el) {
      len = el.value.length;
      normalizedValue = el.value.replace(/\r\n/g, "\n");

      textInputRange = el.createTextRange();
      textInputRange.moveToBookmark(range.getBookmark());

      endRange = el.createTextRange();
      endRange.collapse(false);

      if (textInputRange.compareEndPoints("StartToEnd", endRange) > -1) {
        start = end = len;
      } else {
        start = -textInputRange.moveStart("character", -len);
        start += normalizedValue.slice(0, start).split("\n").length - 1;

        if (textInputRange.compareEndPoints("EndToEnd", endRange) > -1) {
          end = len;
        } else {
          end = -textInputRange.moveEnd("character", -len);
          end += normalizedValue.slice(0, end).split("\n").length - 1;
        }
      }
    }
  }
  return {
    start: start,
    end: end
  };
}

// This is shamelessly copied from http://blog.vishalon.net/index.php/javascript-getting-and-setting-caret-position-in-textarea/
function setCaretPosition(ctrl, pos){
  if(ctrl.setSelectionRange)
  {
    ctrl.focus();
    ctrl.setSelectionRange(pos,pos);
  }
  else if (ctrl.createTextRange) {
    var range = ctrl.createTextRange();
    range.collapse(true);
    range.moveEnd('character', pos);
    range.moveStart('character', pos);
    range.select();
  }
}

// This is my contribution.
$("textarea.editor").live("keydown", function(e) {
  // Turn tab presses into soft-spaces
  if (e.keyCode == 9) {
    e.preventDefault()
    p = getInputSelection(e.target).start
    cv = $(e.target).val()
    $(e.target).val(cv.substr(0, p) + "  " + cv.substr(p))
    setCaretPosition(e.target, p + 2)
  }
  // Make enter preserve indentation of the current line
  else if (e.keyCode == 13) {
    e.preventDefault()
    p = getInputSelection(e.target).start
    cv = $(e.target).val()
    t = ""
    for (i = p; i >= 0; i--) {
      if (cv.substr(i, 1) == "\n") {
        if (p != i || p == 0) {
          t = cv.substr(i, p - i).replace(/\n/g, "").match(/^\s*/)[0]
          break
        }
      }
    }
    $(e.target).text(cv.substr(0, p) + "\n" + t + cv.substr(p))
    setCaretPosition(e.target, p + t.length + 1)
  }
  // Tell backspace to delete two spaces if the only thing before the cursor is blank space divisible by 2
  else if (e.keyCode == 8) {
    p = getInputSelection(e.target).start
    cv = $(e.target).val()
    t = ""
    for (i = p; i >= 0; i--) {
      if (cv.substr(i, 1) == "\n") {
        if (p != i || p == 0) {
          tmp = cv.substr(i, p - i).replace(/\n/g, "").match(/^\s*$/)
          if (tmp) {
            t = tmp[0]
          }
          break
        }
      }
    }
    if (t.length % 2 == 0 && t.length > 0) {
      e.preventDefault()
      $(e.target).val(cv.substr(0, p - 2) + cv.substr(p))
      setCaretPosition(e.target, p - 2)
    }
  }
  // Make Home or Meta+Left hop to the first non-whitespace character on the line
  else if (e.keyCode == 36 || (e.keyCode == 37 && e.metaKey)) {
    p = getInputSelection(e.target).start
    cv = $(e.target).val()
    cl = ""
    cs = 0
    for (i = p - 1; i >= 0; i--) {
      if (cv.substr(i, 1) == "\n") {
        cl = cv.substr(i, p - i)
        cs = cl.match(/^\s*/)[0].length
        break
      }
    }
    e.preventDefault()
    setCaretPosition(e.target, p - cl.length + cs)
  }
})