Scope: Where a Variable Can Be Seen

Scope is the part of a program where a variable can be seen and used, and knowing its three kinds (global, function and block) explains a whole family of "is not defined" errors and values that won't change.

Updated

Cheat sheet: Scope: Where a Variable Can Be Seen
Category
JavaScript
Level
Apprentice
Tags
Block Scope, Global Scope, JavaScript, Local Scope, Scope (javascript), Scope Chain, Shadowing (javascript)