How to check if it's a string or json [duplicate]

Question

I have a json string that is converted from object by JSON.Stringify function.

I'd like to know if it's json string or just a regular string.

Is there any function like "isJson()" to check if it's json or not?

I'd like to use the function when I use local storage like the code below.

Thank you in advance!!

var Storage = function(){}

Storage.prototype = {

  setStorage: function(key, data){

    if(typeof data == 'object'){

      data = JSON.stringify(data);
      localStorage.setItem(key, data);     

    } else {
      localStorage.setItem(key, data);
    }

  },


  getStorage: function(key){

    var data = localStorage.getItem(key);

    if(isJson(data){ // is there any function to check if the argument is json or string?

      data = JSON.parse(data);
      return data;

    } else {

      return data;
    }

  }

}

var storage = new Storage();

storage.setStorage('test', {x:'x', y:'y'});

console.log(storage.getStorage('test'));

Answer 1

The "easy" way is to try parsing and return the unparsed string on failure:

var data = localStorage[key];
try {return JSON.parse(data);}
catch(e) {return data;}