How to send variables from one file to another in Javascript? [duplicate]

You can use cookies, window.name, send data by url as querystring, or through web storage.

In this exaple I'm going to save data from one page and read it from another page using the localStorage - (specs), and the following methods:

• JSON.stringify()
• JSON.parse()
• WindowBase64.btoa()
• WindowBase64.atob()

login.html

function saveData(user, pass) {
   var account = {
     User: user,
     Pass: pass
   };
   //converts to JSON string the Object
   account = JSON.stringify(account);
   //creates a base-64 encoded ASCII string
   account = btoa(account);
   //save the encoded accout to web storage
   localStorage.setItem('_account', account);
}

index.html

function loadData() {
   var account = localStorage.getItem('_account');
   if (!account) return false;
   localStorage.removeItem('_account');
   //decodes a string data encoded using base-64
   account = atob(account);
   //parses to Object the JSON string
   account = JSON.parse(account);
   //do what you need with the Object
   fillFields(account.User, account.Pass);
   return true;
}

Passing the object from one page to another by url as querystring (search)

• Location

login.html

function saveData(user, pass) {
   var account = {
     User: user,
     Pass: pass
   };
   account = JSON.stringify(account);
   account = btoa(account);
   location.assign("index.html?a=" + account);
}

index.html

function loadData() {
   var account = location.search;
   if (!account) return false;
   account = account.substr(1);
   //gets the 'a' parameter from querystring
   var a = (/^a=/);
   account = account.split("&").filter(function(item) {
      return a.test(item);
   });
   if (!account.length) return false;
   //gets the first element 'a' matched
   account = account[0].replace("a=", "");
   account = atob(account);
   account = JSON.parse(account);
   //do what you need with the Object
   fillFields(account.User, account.Pass);
   return true;
}

See an extended answer here: https://stackoverflow.com/a/30070207/2247494