You possibly created the database putting its name in double quotes as "Javascript_Rails_Project_development". Note the upper case letters.
Usually identifiers in SQL are case insensitive. If you quote them in such a way however, they become case sensitive. That is, there is no database named javascript_rails_project_development as the letters are all lower case.
Once created with the name double quotes and including upper case characters you need to address the object afterwards by a name in double quotes with the exact matching cases of the letters.
Try:
DROP DATABASE IF EXISTS "Javascript_Rails_Project_development" ;
And possibly avoid upper case and quoted names in the future all together. It's just making things more complicated in most of the cases.