The JavaScript function presented in this page can be used to add HTML, or BBCode Tag, to selected text in textarea. This function, addTagSel(), receives two arguments: the tag name, and the id of textarea. Returns the selected text, with tag; and points the cursor at the end of selected text in textarea.
- By default, adds HTML tag. To add BBCode, replace: new Array('<', '>'); with: new Array('[', ']'); in the code of the function.

addTagSel() Function Code

// Function to add <tag>To Selected text</tag> in textarea with id of idelm
// Receives the tag name, and the id of textarea.
// Points the cursor at the end of selected text in textarea
// Returns the selected text, with tag
function addTagSel(tag, idelm) {
  // https://CoursesWeb.net/javascript/
  var tag_type = new Array('<', '>');        // for BBCode tag, replace with:  new Array('[', ']');
  var txta = document.getElementById(idelm);
  var start = tag_type[0] + tag + tag_type[1];
  var end = tag_type[0] +'/'+ tag +  tag_type[1];
  var IE = /*@cc_on!@*/false;    // this variable is false in all browsers, except IE

  if (IE) {
    var r = document.selection.createRange();
    var tr = txta.createTextRange();
    var tr2 = tr.duplicate();
    tr2.moveToBookmark(r.getBookmark());
    tr.setEndPoint('EndToStart',tr2);
    var tag_seltxt = start + r.text + end;
    var the_start = txta.value.replace(/[\r\n]/g,'.').indexOf(r.text.replace(/[\r\n]/g,'.'),tr.text.length);
    txta.value = txta.value.substring(0, the_start) + tag_seltxt + txta.value.substring(the_start + tag_seltxt.length, txta.value.length);

    var pos = txta.value.length - end.length;    // Sets location for cursor position
    tr.collapse(true);
    tr.moveEnd('character', pos);        // start position
    tr.moveStart('character', pos);        // end position
    tr.select();                 // selects the zone
  }
  else if (txta.selectionStart || txta.selectionStart == '0') {
    var startPos = txta.selectionStart;
    var endPos = txta.selectionEnd;
    var tag_seltxt = start + txta.value.substring(startPos, endPos) + end;
    txta.value = txta.value.substring(0, startPos) + tag_seltxt + txta.value.substring(endPos, txta.value.length);

    // Place the cursor between formats in #txta
    txta.setSelectionRange((endPos+start.length),(endPos+start.length));
    txta.focus();
  }
  return tag_seltxt;
}

- Example of usage addTagSel() function. Adds tag to selected text in textarea, and displays a message window with the selected text and tag.
<form action="#" method="post">
 <textarea name="my_textarea" id="my_textarea" cols="55" rows="4">Free JavaScript and jQuery Courses, tutorials: https://CoursesWeb.net/javascript/</textarea><br />
 <input type="button" id="addtag" value="AddTag" />
</form>

<script type="text/javascript">
// <![CDATA[
// Function to add <tag>To Selected text</tag> in textarea with id of idelm
// Receives the tag name, and the id of textarea.
// Points the cursor at the end of selected text in textarea
// Returns the selected text, with tag
function addTagSel(tag, idelm) {
  // https://CoursesWeb.net/javascript/
  var tag_type = new Array('<', '>');        // for BBCode tag, replace with:  new Array('[', ']');
  var txta = document.getElementById(idelm);
  var start = tag_type[0] + tag + tag_type[1];
  var end = tag_type[0] +'/'+ tag +  tag_type[1];
  var IE = /*@cc_on!@*/false;    // this variable is false in all browsers, except IE

  if (IE) {
    var r = document.selection.createRange();
    var tr = txta.createTextRange();
    var tr2 = tr.duplicate();
    tr2.moveToBookmark(r.getBookmark());
    tr.setEndPoint('EndToStart',tr2);
    var tag_seltxt = start + r.text + end;
    var the_start = txta.value.replace(/[\r\n]/g,'.').indexOf(r.text.replace(/[\r\n]/g,'.'),tr.text.length);
    txta.value = txta.value.substring(0, the_start) + tag_seltxt + txta.value.substring(the_start + tag_seltxt.length, txta.value.length);

    var pos = txta.value.length - end.length;    // Sets location for cursor position
    tr.collapse(true);
    tr.moveEnd('character', pos);        // start position
    tr.moveStart('character', pos);        // end position
    tr.select();                 // selects the zone
  }
  else if (txta.selectionStart || txta.selectionStart == "0") {
    var startPos = txta.selectionStart;
    var endPos = txta.selectionEnd;
    var tag_seltxt = start + txta.value.substring(startPos, endPos) + end;
    txta.value = txta.value.substring(0, startPos) + tag_seltxt + txta.value.substring(endPos, txta.value.length);

    // Place the cursor between formats in #txta
    txta.setSelectionRange((endPos+start.length),(endPos+start.length));
    txta.focus();
  }
  return tag_seltxt;
}

// registers onclick event to element with id="addtag"
document.getElementById('addtag').onclick = function() {
  // calls the addTagSel() function for "my_textarea", displaying the selected text and tag into an alert window
  var tag_seltxt = addTagSel('tag', 'my_textarea');
  alert(tag_seltxt);
};
// ]]>
</script>
Demo (select text in textarea, then click the AddTag button):

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Add Tag to Selected Text in textarea with JavaScript

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