code: function setItem( key, value ) {
        const nsKey = `${namespace}.${key}`;
        if( value === undefined ) {
           backend.removeItem( nsKey );
        }
        else {
           backend.setItem( nsKey, JSON.stringify( value ) );
        }
     }
docs: ///////////////////////////////////////////////////////////////////////////////////////////////////////// 
  Sets a `value` for a `key`. The value must be JSON serializable. An existing value will be overwritten.
  
  @param {String} key
  the key of the item to set (without namespace prefix)
  @param {*} value
  the new value to set
  
  @memberof StorageApi