Sams Teach Yourself JavaScript in 24 Hours

Testing Multiple Conditions with `if` and `else`

You can now create an example script using if and else. In Hour 2, "Creating Simple Scripts," you created a script that displays the current date and time. This example will use conditions to display a greeting that depends on the time: "Good morning," "Good Afternoon," "Good Evening," or "Good Day". To accomplish this, you can use a combination of several if statements:

if (hours < 10) document.write("Good morning.");
else if (hours >= 14 && hours <= 17) document.write("Good afternoon.");
else if (hours >= 17) document.write("Good evening.");
else document.write("Good day.");

The first statement checks the hours variable for a value less than 10in other words, it checks whether the current time is before 10:00 a.m. If so, it displays the greeting "Good morning."

The second statement checks whether the time is between 2:00 p.m. and 5:00 p.m. and, if so, displays "Good afternoon." This statement uses else if to indicate that this condition will only be tested if the previous one failedif it's morning, there's no need to check whether it's afternoon. Similarly, the third statement checks for times after 5:00 p.m. and displays "Good evening."

The final statement uses a simple else, meaning it will be executed if none of the previous conditions matched. This covers the times between 10:00 a.m. and 2:00 p.m. (neglected by the other statements) and displays "Good day."

The HTML File

To try this example in a browser, you'll need an HTML file. We will keep the JavaScript code separate, so Listing 7.1 is the complete HTML file. Save it as timegreet.html but don't load it into the browser until you've prepared the JavaScript file in the next section.

Listing 7.1. The HTML File for the Time and Greeting Example

<html> <head><title>if statement example</title></head> <body> <h1>Current Date and Time</h1> <p> <script language="JavaScript" type="text/javascript" src = "timegreet.js"> </script> </p> </body> </html>

The JavaScript File

Listing 7.2 shows the complete JavaScript file for the time greeting example. This uses the built-in Date object functions to find the current date and store it in hours, mins, and secs variables. Next, document.write statements display the current time, and the if and else statements introduced earlier display an appropriate greeting.

Listing 7.2. A Script to Display the Current Time and a Greeting

// Get the current date now = new Date(); // Split into hours, minutes, seconds hours = now.getHours(); mins = now.getMinutes(); secs = now.getSeconds(); // Display the time document.write("<h2>"); document.write(hours + ":" + mins + ":" + secs); document.write("</h2>"); // Display a greeting document.write("<p>"); if (hours < 10) document.write("Good morning."); else if (hours >= 14 && hours <= 17) document.write("Good afternoon."); else if (hours > 17) document.write("Good evening."); else document.write("Good day."); document.write("</p>");

To try this example, save this file as timegreet.js (or download it from this book's website) and then load the timegreet.html file into your browser. Figure 7.1 shows the results of this script.

Figure 7.1. The output of the time greeting example, as shown by Internet Explorer.

[View full size image]

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Main Menu

Sams Teach Yourself JavaScript in 24 Hours
Table of Contents
Copyright
About the Author
Acknowledgments
Part I: Introducing the Concept of Web scripting and the JavaScript Language
Part II: Learning JavaScript Basics
	Hour 5. Using Variables, Strings, and Arrays
	Hour 6. Using Functions and Objects
	Hour 7. Controlling Flow with Conditions and Loops
		The if Statement
		Using Shorthand Conditional Expressions
		Testing Multiple Conditions with if and else
		Using Multiple Conditions with switch
		Using for Loops
		Using while Loops
		Using do…while Loops
		Working with Loops
		Looping Through Object Properties
		Summary
		Q&A
		Quiz Questions
		Quiz Answers
		Exercises
	Hour 8. Using Built-in Functions and Libraries
Part III: Learning More About the DOM
Part IV: Working with Advanced JavaScript Features
Part V: Building Multimedia Applications with JavaScript
Part VI: Creating Complex Scripts
Part VII: Appendixes
Index

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