SCOPE CHAIN VS. CALL STACK

CALL STACK

Order in which functions were called

 

SCOPE CHAIN

Order in which functions are written in the code has nothing to do with order in which functions were called!

 

SUMMARY

• Scoping asks the questions "Where do variables live?" or "Where can we access a certain variable, and where not?";
• There are 3 types of scope in JavaScript: the global scope, scopes defined by functions, and scopes defined by blocks;
• Only let and const variables are block-scoped. Variables declared with var end up in the closest function scope;
• In JavaScript, we have lexical scoping, so the rules of where we can access variables are based on exactly where in the code functions and blocks are written;
• Every scope always has access to all the variables from all its outer scopes. This is the scope chain!
• When a variable is not in the current scope, the engine looks up in the scope chain until it finds the variable it's looking for. This is called variable lookup;
• The scope chain is a one-way street; a scope will never, ever have access to the variables of an inner scope;
• The scope chain in a certain scope is equal to adding together all the variable environments of the all parent scopes;
• The scope chain has nothing to do with the order in which functions were called. It does not affect the scope chain at all!