Difference in closure working for the following codes

Question

function getData() {
  console.log('Fetching data');
}

const magic = (fn, delay) => {
  let timer;
  return function() {
    clearTimeout(timer);
    timer = setTimeout(() => {
      fn();
    }, delay);
  }
}

const better = magic(getData, 3000);

<input type="text" onkeypress="better()" />

In this code if we press a key only once lets say now timer value is 1.After that again we press a key then the clearTimeout(1) will happen and after 3s output will be printed. But if we consider this code

function a() {
  let count = 0;
  return function b() {
    count = count + 1;
    console.log(count);
  }
}
a()();
a()();

Here ideally when first a is called count should be updated to 1. After second a is called count should be 2 right because count is stored in heap memory?

Answer 1

When you call a() you define a new variable called count and assign 0 to it.

When you call the return value as a function, you increment count and log it.

---

You are calling a() twice, so you create a new count with a value of 0 each time.

---

Compare:

function a() {
  let count = 0;
  return function b() {
    count = count + 1;
    console.log(count);
  }
}

const first_return_value_from_a = a();
const second_return_value_from_a = a();
first_return_value_from_a();
second_return_value_from_a();

and

function a() {
  let count = 0;
  return function b() {
    count = count + 1;
    console.log(count);
  }
}

const return_value_from_a = a();
return_value_from_a();
return_value_from_a();