IIFE (Immediately Invoked Function Expression)

var value = 'global';

(function() {
  var value = 'local';
  console.log(value);
})();

console.log(value);

global, global
local, global
The output will be 'local' followed by 'global'. This demonstrates variable shadowing and scope isolation. Inside the IIFE, a new 'value' variable is declared with 'var', which shadows (hides) the global 'value' variable. When console.log(value) is called inside the IIFE, it refers to this local variable and prints 'local'. After the IIFE completes, the second console.log(value) executes in the global scope, where 'value' is still 'global', so it prints 'global'. This example shows how IIFEs create their own variable scope, preventing local variables from affecting variables in the outer scope even if they have the same name. This isolation is key to writing modular code that doesn't have unexpected side effects.
global, local
local, local