SOURCE

function parseParam (param, key){ 
   var paramStr=""; 
   if(param instanceof String || param instanceof Number || param instanceof Boolean){ 
	     paramStr += "&" + key + "=" + encodeURIComponent(param); 
   } else { 
	     $.each(param,function(i){
	    	   var k = key == null ? i : key + (param instanceof Array ? "["+i+"]" : "."+i)
	    	   paramStr += '&' + parseParam(this, k)
	     })
   }
   return paramStr.substr(1); 
}

var obj = {
    a: '123',
    b: 'koa'
}

parseParam(obj) // 'a=123&b=koa'