[JS] IIFE (Immediately Invoked Function Expression)

IIFE (Immediately Invoked Function Expression) in JavaScript runs immediately when it defined.

const firstIIFE = (function () {
  var score = Math.random() * 10;
  console.log("First: ", score >= 5);
})();

// Normal Function
function notIIFE() {
  var score = Math.random() * 10;
  console.log("Second: ", score >= 5);
}
notIIFE();

// It is possible to pass paramester when it executed
(function secondIIFE(luckynum) {
  var score = Math.random() * 10;
  console.log("Second: ", score >= 5 - luckynum);
})(5);

notIIFE();
console.log(firstIIFE); // undefined

You can use this feature to make private/public variables and methos in it.

const test_module = (function() {
    const p_value = "Access";
    const privateFunction = function() {
        console.log(p_value);
    }
    return {
        publicFunction : function() {
            console.log("This is a public function: ", p_value);
        }
    }
})();

test_module.publicFunction();
test_module.privateFunction(); // Not function