javascript - JSON string parameter not working -

i'm having trobule json parameter. here's part of code:

<script type="text/javascript">     $("#deco").click(function () {         var cap = document.getelementbyid('canvasvideo').todataurl();          var canvas = document.getelementbyid('captimage');         var context = canvas.getcontext('2d');         var imageobj = new image();          imageobj.onload = function () {             context.drawimage(imageobj, 0, 0);         };         imageobj.src = cap;         //var cap = 'hardcoding' ; if hardcode text, , pass parameter, works.          $.getjson('/home/decodeqr', { img : cap  },             function (iddonante) {                 document.getelementbyid("result").value = iddonante;             });         });  </script> 

in server side, i've got following:

    [acceptverbs(httpverbs.get)]     public jsonresult decodeqr(string img)     {          var iddonante = getidqr(conversion.base64stringtobitmap(img));          return json(iddonante, jsonrequestbehavior.allowget);     } 

as mentioned in code, if hardcode parameter works. think problem in variable gets string canvas.todataurl(), not sure.

edit: have mention, now, jsonresult method on server never called, unless hardcode img attribute.

there limit how long url can be. see here: what maximum length of url in different browsers?

you should posting encoded image data server instead.