The let keyword was introduced in ES6 (2015)
Variables declared with let have Block Scope
Variables declared with let must be Declared before use
Variables declared with let cannot be Redeclared in the same scope
Block Scope
Before ES6 (2015), JavaScript did not have Block Scope.
JavaScript had Global Scope and Function Scope.
ES6 introduced the two new JavaScript keywords: let and const. Continue reading JavaScript Let