What is the difference between var and let in Typescript?

Question

I submitted a question on stack overflow asking how I could stop the putTestQuestionResponses() function from executing IF a previous version was already executing.

Answer 1

example:

// demo: var
for(var i =0 ; i<5 ; i++){
   console.log(i) 
}//finally i =5
console.log(i) // i=5

// demo: let 
for(let i = 0; i<5;i++){
   console.log(i)
}
console.log(i)// i is undefined