```js
    function diffSign(div) {
      var sign = document.getElementById(div.id);
      if (XXXXX) {
        XXXXX
      } else {
        XXXX
      }
    }
```

```html
<div data-toggle="collapse" data-target="#demo@(i.tostring)" id="Sign@(i.ToString)" onclick=diffSign(this)>+</div>
```

I want to change + sign to - and can change back!
THX