What is the difference between using variables declared with var and let in the context of closures?

The main difference lies in the scope they create and, consequently, how they affect the value of the variable captured by the closure.

Variables declared with var have function or global scope. In a loop, for example, the closure captures the last value of the var variable due to hoisting.

// Example with var
for (var i = 0; i < 3; i++) {
  setTimeout(function() {
    console.log(i); // Will output 3 three times
  }, 100);
}

Variables declared with let have block scope. In a loop, let creates a new variable for each iteration, and the closure captures the value of the variable for that specific iteration.

// Example with let
for (let j = 0; j < 3; j++) {
  setTimeout(function() {
    console.log(j); // Will output 0, 1, 2
  }, 100);
}

In the context of closures, this means that a closure capturing a var variable will refer to the same memory location containing the last value of the variable. A closure capturing a let variable will refer to a separate memory location for each iteration of the loop.