Question

Is it possible to add a subscript tag to numbers as a user types into an textbox, for example if a user was to type in H20 it would instantly of converted to H₂0. I am looking for a solution using jQuery?

Answer 1

No, textboxes may not contain html-markup. But you can replace the 2 with a subscript-2-character ₂ (Unicode 2082 ).

Here the function :

function fx(e)
{
  var k=String.fromCharCode(e.which);

  if(k.match(/\d/))
  {
    var r=String.fromCharCode(8320+Number(k));
    try{//IE
          document.selection.createRange().text=r;
         }
      catch(x)
      {//others
        var o         = e.target
        var intStart  = o.selectionStart;
        var intEnd    = o.selectionEnd;
        o.value = (o.value).substring(0, intStart) + r + 
                  (o.value).substring(intEnd, o.value.length);
                    o.selectionStart=o.selectionEnd=intStart+r.length;
                    o.focus();
      }  
      return false;
  }
  return true;
} 

Call this function onkeypress.

It replaces(if a number was typed) the current selection with the subscript of that number.
Unicode-char at position 8320(HEX 2080) is subscript-zero, it just adds the typed number to that position and retrieves the char at the new position.

Demo: http://jsfiddle.net/doktormolle/KDgH9/