Having problem in understanding callback functions and assigning functions to variables

Program #1:-function placeOrder(orderNumber) { console.log('Order Number :', orderNumber);cookAndDeliver(function() { console.log('Delivered order :', orderNumber); }); };function cookAndDeliver(callback) { setTimeout(callback, 3000); };placeOrder(1); placeOrder(2); placeOrder(3);Output:- Order Number : 1 Order Number : 2 Order Number : 3<3 seconds delay>Delivered order : 1 Delivered order : 2 Delivered order : 3Program #2:-function placeOrder(orderNumber) { console.log('Order Number :', orderNumber);cookAndDeliver(function() { console.log('Delivered order :', orderNumber); }); };function cookAndDeliver(callback) { setTimeout(callback(), 3000); };placeOrder(1); placeOrder(2); placeOrder(3);Output:- Order Number : 1 Delivered order : 1 Order Number : 2 Delivered order : 2 Order Number : 3 Delivered order : 3<3 seconds delay>In program #1 'callback' is passed. In program #2 'callback()' is passed.What is the difference in 'callback' and 'callback()' ?? Why is the output different??

Submitted April 26, 2016 at 06:49PM by pranjalworm