let totalPrice = coursePrice * 1.18;     //---------

                                         //         | ------>  this is TDZ for coursePrice

                                         //         |

console.log(totalPrice);                 //---------

​

let coursePrice = 699;

What is the Temporal Dead Zone?

​

This is what the TDZ is: the term to describe the state where variables are 

un-reachable. They are in scope, but they aren't declared.

​

The let and const variables exist in the TDZ from the start of their enclosing 

scope until they are declared.

​

You could also say that the variables exist in the TDZ from the place they get 

bound (when the variable gets bound to the scope it's inside) until it is 

declared (when a name is reserved in memory for that variable).