How can I get the key value in a JSON object?

JSON content is basically represented as an associative array in JavaScript. You just need to loop over them to either read the key or the value:

    var JSON_Obj = { "one":1, "two":2, "three":3, "four":4, "five":5 };

    // Read key
    for (var key in JSON_Obj) {
       console.log(key);
       console.log(JSON_Obj[key]);
   }