Q:

LocalStorage - detect if local storage is already full

is there a way to detect if local storage has reached its maximum value to store? 
Or at least something like an error message that tells that i can't store anymore because i have reached the maximum size?   I want to catch this so i can remove the oldest items in my local storage and insert new ones.  
I am using local storage to store some of my queries from my database so users would be able to load them immediately if that specific item exist on local storage.  if not then, that is the time i retrieve the data in the server.  

A:

Upon attempting to add to localstorage, if there is not enough space, this error will be thrown.  In you particular scenario, you could use this event to free up some space. 
try {
  localStorage.setItem("name", "Hello World!");  //saves to the database, "key", "value"
} catch (e) {
  if (e == QUOTA_EXCEEDED_ERR) {
    alert('Quota exceeded!');  //data wasn't successfully saved due to quota exceed so throw an error
  }
}

credit to - http://chrisberkhout.com/blog/localstorage-errors/

