get
    weakReferenceMap.get(key)
  
  Returns the value stored at key if it's in the store.
Parameters
- key 
{String}:The key of the item in the store.
 
Returns
 {*|undefined}: 
The item if it's available.
weakReferenceMap.get(key)
  Returns the value stored at key if it's in the store.
{String}: The key of the item in the store.
 {*|undefined}: 
The item if it's available.