You can use the JSON.parse() for that.

See docs at MDN

Example:

var myObj = JSON.parse('{"p": 5}');
console.log(myObj);

You can use:

JSONObject jsonObject = new JSONObject();
jsonObject.toString();

And if you want to get a specific value, you can use:

jsonObject.getString("msg");

or Integer value

jsonObject.getInt("codeNum");

For long Integers

jsonObject.getLong("longNum");

To anyone still looking for an answer:

JSONParser parser = new JSONParser();
JSONObject json = (JSONObject) parser.parse(stringToParse);

It looks like you're trying to deserialize to a raw object. You could create a Class that represents the object that you're converting to. This would be most useful in cases where you're dealing with larger objects or JSON Strings.

For instance:

  class Test {

      String test; 

      String getTest() { return test; }
      void setTest(String test) { this.test = test; }

  }

Then your deserialization code would be:

   JavaScriptSerializer json_serializer = new JavaScriptSerializer();
   Test routes_list = 
          (Test)json_serializer.DeserializeObject("{ \"test\":\"some data\" }");

More information can be found in this tutorial: http://www.codeproject.com/Tips/79435/Deserialize-JSON-with-Csharp.aspx

The jQuery method is now deprecated. Use this method instead:

let jsonObject = JSON.parse(jsonString);

Original answer using deprecated jQuery functionality:

If you're using jQuery just use:

jQuery.parseJSON( jsonString );

It's exactly what you're looking for (see the jQuery documentation).