function isJson(obj) { var isjson = typeof(obj) == "object" && Object.prototype.toString.call(obj).toLowerCase() == "[object object]" && !obj.length; return isjson; } isJson(JSON.parse('{}'))//true isJson((new Function("return {}"))())//true isJson(JSON('{}'))//error isJson(eval('{}'))//false isJson(evel('{}'))//error