Scope determines the visabilityand accessibility of variables. It is a set of riles that define which parts of our program are able
to interact with particular variables. There are 2 types of scope: Global and Block. Variables declared outside a function is global
scope and variables declared insidie are within the block scope. With block scope, variables can only be accessed from within the
block whereas, with the global scope, all scripts and functions on a web page can access the variable.

Global variables should be avoided because they tend to make unintended side effects in a program more likely. This almost always
generates code that becomes indeterminate, which returns one value sometimes
and another value at other times. This makes it very difficult to track down bugs.

Strict mode is a setting applied at the top of a JS file. Strict mode makes it so thtat any time a variable is declared without let
or const keyword, an error will be triggered. Strict mode ensures there is no use of global variables in your code.

A side effect is when a function reaches outside its local scope up into a parent scope and alters a value that lives there. A pure
function is when your code is both determinate and has no side effects.