IIFE (Immediately Invoked Function Expression)

What will the counter function created by this IIFE output when called three times in sequence?

var counter = (function() {
  var count = 0;
  return function() {
    return ++count;
  };
})();

console.log(counter());
console.log(counter());
console.log(counter());

1, 1, 1
0, 1, 2
1, 2, 3
The output will be 1, 2, 3. This code demonstrates a common use case for IIFEs: creating a closure with private state. The IIFE defines a private variable 'count' initialized to 0, and returns a function that increments and returns this count. The returned function is assigned to 'counter'. When 'counter' is called, it accesses the 'count' variable in its closure scope, increments it, and returns the new value. Each call to 'counter()' increases 'count' by 1, resulting in the sequence 1, 2, 3. This pattern is often called the 'module pattern' or a 'revealing module pattern' and allows for creating private variables that persist between function calls but cannot be accessed directly from outside.
undefined, undefined, undefined

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