Hoisting & TDZ.
Variables declared with var are hoisted to the top of their function and initialized with undefined. let/const have a temporal dead zone (TDZ) where they cannot be used.
Hoisting with var:
Temporal Dead Zone with let/const:
Variables declared with var are hoisted to the top of their function and initialized with undefined. let/const have a temporal dead zone (TDZ) where they cannot be used.
Hoisting with var:
Temporal Dead Zone with let/const: