let & const

• doesn't hoist
• block scoped

let:

• cannot be accessed before declaration/initialisation

const:

• cannot reassign
• object properties can be reassigned / added / removed

Lexical scope

• describes how a parser resolves variable names when functions are nested.
• The word lexical refers to the fact that lexical scoping uses the location where a variable is declared within the source code to determine where that variable is available.
• Nested functions have access to variables declared in their outer scope.