Recognize when writing in between two $$ signs

问题

I have a textfield in which I'm writing some text.

For the sake of simplicity, I want that alert('Boom!') jumps out every time I start writing in between two $$.

For example I have a blank textfield and start typing (cursor is "|" sign)

Today is a really nice day|

nothing happens, start typing

Today is a really nice day, $|$

still nothing, but now when I start typing

Today is a really nice day, $someText|$

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

Why do I need that kind of feature? I want live-equation-preview (MathJax rendering) every time user starts typing his/her equation, and I can recognize it's an equation by $$ signs (everything in between is rendered).

EDIT: Multiple $$'s are possible in textfield. Script must recognize the one which is currently active (cursor position is between it's $$'s).

回答1:

You can use jQuery caret plugin

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

note: edit and delete these characters Ôªø from line 8

and replace funcition. ( not to replace anything but to use the 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 to do it. You can improve this.

use

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

for a better result.

来源：https://stackoverflow.com/questions/9649857/recognize-when-writing-in-between-two-signs

标签

jquery

mathjax