Set text-cursor position in a textarea

you can use these 2 functions below written by Jamie Munro (setSelectionRange() & setCaretToPos()):

function setSelectionRange(input, selectionStart, selectionEnd) {
    if (input.setSelectionRange) {
        input.focus();
        input.setSelectionRange(selectionStart, selectionEnd);
    }
    else if (input.createTextRange) {
        var range = input.createTextRange();
        range.collapse(true);
        range.moveEnd('character', selectionEnd);
        range.moveStart('character', selectionStart);
        range.select();
    }
}

function setCaretToPos (input, pos) {
       setSelectionRange(input, pos, pos);
}

EXAMPLE:

for example, if you want to set the caret at the end of your textarea you can have this: setCaretToPos(document.getElementById('textarea'), -1);

After refocusing the textarea with txtarea.focus(), add this line:

txtarea.selectionEnd= end + 7;

That will set the cursor seven positions ahead of where it was previously, which will take [b][/b] into account.

Example

document.getElementById('bold').addEventListener('click', boldText);

function boldText() {
  var txtarea = document.getElementById("editor_area");
  var start = txtarea.selectionStart;
  var end = txtarea.selectionEnd;
  var sel = txtarea.value.substring(start, end);
  var finText = txtarea.value.substring(0, start) + '[b]' + sel + '[/b]' + txtarea.value.substring(end);
  txtarea.value = finText;
  txtarea.focus();
  txtarea.selectionEnd= end + 7;
}

#editor_area {
  width: 100%;
  height: 10em;
}

<button id="bold">B</button>
<textarea id="editor_area"></textarea>

if you are using jquery you can do it like this.

$('textarea').prop('selectionEnd', 13);