javascript scoping

Scoping = the organisation and access of variables

Lexical scoping - where scoping is controlled by how functions and blocks are placed in the code e.g. a function inside another function has access to the variables from the first function.

Scope = the space or environment where the variable is declared

• global scope - top-level code variables are available everywhere e.g. var
• function scope - also known as local scope variables are only available inside the function. If attempting to access outside of the function there will be a reference error.
• block-level scoping - this as introduced in ES6 and is only available to variables declared with let and const

Note: ES6 in strict mode functions are also block-scoped

Variable lookup in scope chain to parent scope. This only works with parent scope this does not work the other way round with child scope.