Storage.setItem()
  The setItem() method of the Storage
  interface, when passed a key name and value, will add that key to the given
  Storage object, or update that key's value if it already exists.
Syntax
storage.setItem(keyName, keyValue);
Parameters
Return value
Exceptions
  setItem() may throw an exception if the storage is full. Particularly, in
  Mobile Safari (since iOS 5) it always throws when the user enters private mode. (Safari
  sets the quota to 0 bytes in private mode, unlike other browsers, which allow storage in
  private mode using separate data containers.) Hence developers should make sure to
  always catch possible exceptions from setItem().
Example
The following function creates three data items inside local storage.
function populateStorage() {
  localStorage.setItem('bgcolor', 'red');
  localStorage.setItem('font', 'Helvetica');
  localStorage.setItem('image', 'myCat.png');
}
Note: To see this used within a real world example, see our Web Storage Demo.
Specifications
| Specification | 
|---|
| HTML Standard # dom-storage-setitem-dev | 
Browser compatibility
BCD tables only load in the browser