How to restrict user from deleting words with special characters from textbox

Question

I am working in email CMS using ckeditor.net. At runtime user can change the body of email, I want to restrict user deleting all special words starting with @@ .

Here is example-

Email Alert! :<br />
<br />
**@@Comments**<br />
<br />
Please do not reply to this email.

I don't want user to delete "@@comments" word and all "@@" characters in other email templates . Can you give any code in JavaScript?

At run time I replace "@@" words with some paragraph.

Answer 1

I haven't tested this code (just free-formed it into this response), but here's what I'd do.

On the keydown method of the text input, you need to listen for the backspace key:

var input = document.getElementById('myInput');

input.onkeydown = function() {
    var key = event.keyCode || event.charCode;

    // Detect Backspace (8) & Delete (46) keys
    if( key == 8 || key == 46 ){

       var caretPos = getCaretPos(input);

       // Read backward from the caret position
       // until you hit a space or index 0:
       while ( (input.value[caretPos] != " ") && (caretPos > 0)  ){
          caretPos--;
       }

       // Once you hit the space or index 0, read forward two characters 
       // to see if it === "@@".  If both chars are "@", cancel 
       // the keydown event.  You should probably do some bounds checking
       // here.  Could also be done with String.subtring
       if ( input.value[(caretPos + 1)] == "@" && 
            input.value[(caretPos + 2)] == "@" )
       {
          return false;
       }
    }

};


function getCaretPos(input) {
    // Internet Explorer Caret Position (TextArea)
    if (document.selection && document.selection.createRange) {
        var range = document.selection.createRange();
        var bookmark = range.getBookmark();
        var caret_pos = bookmark.charCodeAt(2) - 2;
    } else {
        // Firefox Caret Position (TextArea)
        if (input.setSelectionRange)
            var caret_pos = input.selectionStart;
    }

    return caret_pos;
}

References

Detect Backspace

Get Caret Position

Cancel the keydown event