Answer for scope

Answers to scope

1. Scope is the range where variables are defined and validated. Global scope is the environment 
where variables are available everywhere in this project. 
Local scope is a particular area where variables are vaildated, for example, a function or a file.
2. We have to avoid global variables to aviod misrable bugs.
3. In strict mode, you cannot use a variable without defined it first.
4. Side effects is that one function's output will affect other functions. 
Pure funtion is that this function is both determinate and has no side affect.