I am trying to learn JSON, i learned that any javascript object with the key in double quotes are considered as JSON object.
And i constructed this object
You are creating a Javascript Object. If you want a JSON-string from it, use JSON.stringify.
So
var myObj = {mykey: "my value"}
,myObjJSON = JSON.stringify(myObj);
Based on comments:
There is no such thing as a JSON Object. There are JSON-strings, which can be parsed to Javascript Objects. Javascript Objects can be stringified to JSON strings. Within a JSON-string keys and values are quoted. So the result of the above is a string containing '{"mykey":"my value"}'.
Try parsing myObjJSON in your browser console (using: JSON.parse(myObjJSON)) and you get: Object {mykey: "my value"}.