What are immediately invoked function expressions (IIFEs) ?

var counter = (function () {  var num = 0;  function increaseNumber() {    num++;  }  function decreaseNumber() {    num--;  }  return {    getNum: function () {      return num;    },    inc: increaseNumber,    dec: decreaseNumber,  };})();// the inital value of num is 0console.log(counter.getNum());counter.inc(); // num is 1counter.inc(); // num is 2counter.inc(); // num is 3// this technique gives you the ability to hide // state inside the function closureconsole.log(counter.getNum());