Variable scope questions and answers

Variable scope questions and answers

What is scope? Your explanation should include the idea of global vs. block scope.

Scope describes where and when a variable can be accessed in code. 
Global scope is available anywhere in the code, whereas block is only available in a specific function or situation.


Why are global variables avoided?

Global variables can cause functions to be indeterminate, which means that they can have the same input and produce different results.
They can also cause code to behave in unexpected ways and make debugging difficult.


Explain JavaScript's strict mode

Strict mode does not allow global variables (eg, "dog = 123") and forces one to use var, let or const.


What are side effects, and what is a pure function?

A side effect is when a function affects something outside its own scope, and in its parent scope.
A pure function is one that is determinate (same input always produces same output) and has no side effects.