jquery - Recognize when writing in between two $$ signs -

i have textfield in i'm writing text.

for sake of simplicity, want alert('boom!') jumps out every time start writing in between 2 $$.

for example have blank textfield , start typing (cursor "|" sign)

today nice day| 

nothing happens, start typing

today nice day, $|$ 

still nothing, when start typing

today nice day, $sometext|$ 

alert box should jump out each letter in between dollar signs.

why need kind of feature? want live-equation-preview (mathjax rendering) every time user starts typing his/her equation, , can recognize it's equation $$ signs (everything in between rendered).

edit: multiple $$'s possible in textfield. script must recognize 1 active (cursor position between it's $$'s).

you can use jquery caret plugin

http://examplet.buss.hk/download/download.php?plugin=caret.1.01

note: edit , delete these characters Ôªø line 8

and replace funcition. ( not replace use index of matched pattern )

$("#mytext").bind("keyup", function(e){      var text = $(this).val();      var caret = $(this).caret().start;       if(text && text.length > 0){         text.replace(/\$.*?\$/g, function(m, n){            if(caret > n && caret < (n + m.length)){               alert("boom");            }         });      } }); 

demo : http://jsfiddle.net/xqxxb/

just showing how it. can improve this.

use

$("#mytext").bind("keyup keydown change", function(e){ ... 

for better result.