closures.js

function A() {
  const msgFromOuterFn = 'I am from Outer function scope';
  function B() {
    console.log(msgFromOuterFn);
  }
  return B;
}
// A returns a function B, In JavaScript when ever any function completes its execution, its scope is removed from the heap. So all the variables declared in its scope won't be available once its execution is done.
const returnedFn = A();
// A() completed its execution, so the value msgFromOuterFn will not able available.
// With JS Closures, even the outer function completed execution, inner functions are able to access the outer functions scope.
console.log(returnedFn());
// Will print its value, instead of throwing an error