Object: Objects are collection of properties in a hierarchy.
Five built-in objects in JavaScript:
1.Window.prompt()
2.window.alert()
3.Math.floor()
4.Math.max()
5.document.write()

Regular Expression is an object that describes the pattern of characters.
Regular expressions are used to perform pattern-matching and "search-and-replace" functions on text.

Math.round(): The round() method of Math Objects rounds the numeric data to the nearest integer.
Math.floor(): The floor() method of Math objects returns the input data, rounded downwards to the nearest integer.
Math.ceil(): The ceil() method of Math objects returns the input data, rounded upwards to the nearest integer.

An undefined value is returned when we attempt to use a variable that has not been defined or that is declared but that we forgot to provide with a value.
On the otherhand, null value is returned when we declare and define a variable as null if we want absolutely nothing in it but we don't want it to be undefined.

Alert(): The alert() function displays a message on the web page for the users. In this case the users need nothing to do except click to close to it.
prompt(): The prompt() function also displays a message/statements for the users but in this the users can also input data in the input box.