Scope is the tiered system by which variables can be accessed in a program. When a variable is called for from
inside a function, the program will look for that variable first within the function, then withing the parent function
if not found, and so on until it finds the variable. Variables contained withing function are said to have local
scope, as they can only be called withing that function. On the other hand, varibales that are declared outside of any
function are are said to have global scope, as they can be called and manipulated from anywhere withing the program,
even across files.

  Variables with global scope ('globals') are especially tricky when considering 'hoisting', which refers to the way
in which JavaScript program variables are declared within their scope before the pogram is run. If a global variable is
being declared within a function, it coud be altered from within other functions before the program even runs. Global
varibales are best avoided, becuase of their open accessability they can be tricky to manage and changing them could
have unintended side effects.

  Unintended side effects happen when the programmer creates a variable within  function that has the same name as a
global variable and doesn't use the 'var' keyword to signify that it is separate. This causes the function to reach
outside of it's scope and alter the global variable, thereby rendering the program indeterminate. A function is
considered 'pure' when it is determinate and has no side effects. JavaScript offeres a useful tool to help programmers
avoid unintended side effects called 'strict' mode. When 'strict' is activated, it raises an error whenever the user
declares a variable without the 'var' keyword, the one surefire way to prevent unintedned side effects.