simple way to store data in js

You want a simple way to store data? In javascript, you can use window.localStorage.
localStoge allows you store any information in browser. It is new feature of HTML5, and using method is similar to hashmap(with key and value). To store data, use this syntax:

localStorage.setItem(key, value);

And to get data, use:

localStorage.getItem(key);

localStorage also provide method to delete data:

localStorage.removeItem(value); //delete one
localStorage.clear(); //delete all

Read more about document: https://developer.mozilla.org/en-US/docs/Web/API/Window/localStorage
Because it's pretty basic and simple, localStorage only store string data, if data is more complex, it becomes useless. Addition, the limit of data is small(about 5mb); and it has not security. Therefore, think carefully before use localStorage.