Decision Making in JavaScript

The assignment operator,=, is different from the equality operator (double equal),==. The following table shows the equality, relational and logical operators used in JavaScript:

Equality and relational operators

			Relational operator		Example in JavaScript		Meaning 
== a==b a equal to b
=== a===b a equal to b value and type (for example: assume a = 9; a=== 9 is true but a==='9' is false)
!= a!=b a is not equal to be
> a>b a is greater than be
< a<b a is less than be
>= a>=b a is greater or equal to be b
<= a<=b a is less or equal to be

Logical operator Meaning Example in JavaScript && and (a < 7 && b > 5)
|| or (a < 7 || b > 5)
! not !(a == b)

If statement

The next example shows how If statements are used to display greetings based on the current time of the day:
	<!DOCTTYPE html> 
<!--Example 1: If Statement and relational operators.html -->
<title> If Statement and relational operators </title>
<script >
var user_name = window.prompt("Please enter your name");
var c_time = new Date(); //current date and time
var c_hour = c_time.getHours(); //current hours (0-23)
//let's find out if it's morning from the 1st test
if (c_hour <12) document.write('<h2> Good Morning! </h2>'+ user_name + '</h2>');
//let's find out if it's afternoon/evening
if (c_hour >=12)
//let's see if the time is within afternoon and before evening
c_hour = c_hour-12;
if (c_hour < 6)
document.write('<h2> Good Afternoon! '+ user_name + '</h2>');
if (c_hour >= 6)
document.write('<h2> Good Evening! </h2>'+ user_name + '</h2>');
} //end if
// -->
See here a demo where time entered is in the afternoon:

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Date of last modification: March 26, 2019.