The Alert and Prompt Built-In Functions

 

Introduction.  As with most every programming language, there are built-in functions.  In this page we will focus on two main types.
  • alert - to open message boxes to the user
  • prompt - input boxes to get information from the user

These are really quite similar to the MsgBox and InputBox from Visual Basic, but they have the added advantage of opening in a web browser. 

The Alert( ) Function.  First we will make use of the alert( ) function.  It's setup to give a message in a box with an OK button.  You can get a new line within the message by using the "\n" within the message.  You need to copy the following code into a file called AlertSecondsPerDay.html.  This will just produce an alert for each of the input constants before producing the result on the web page after this page is uploaded and accessed.

 

<html>
<head>
<title>Seconds in a Day</title>

<script language="JavaScript">

var SecondsPerMinute = 60;
var MinutesPerHour = 60
var HoursPerDay = 24;

// echoing these variables
alert("There are " + SecondsPerMinute + " seconds per minute");
alert("There are " + MinutesPerHour + " minutes per hour");
alert("There are " + HoursPerDay + " hours per day");

var SecondsPerDay = SecondsPerMinute*MinutesPerHour*HoursPerDay;

</script>
</head>

<body bgcolor = "000044" text = "aaaaaa">

<H1>By my calculations</H1>
<font size = 4>
<script language="JavaScript">

var FirstPart = "There are ";
var LastPart = " seconds in a day.";
var WholeThing = FirstPart + SecondsPerDay + LastPart;

window.document.write(WholeThing);

</script>
</font>

</body>
</html>

 

While the script is executing as the page is loading you should get three alert( ) boxes that look similar to the following.

 

 

The Prompt( ) Function.  Now we will modify what we have done so far to get rid of the irritating alert( ) functions, but get some input from the user so that the program will calculate the number of seconds in a number of days entered by the user.  The prompt(message,default) function allows you to display a message and a default value within the prompt box.

You should name the file HowManySecondsPerDays.html.

 

<html>
<head>
<title>Seconds in a Day</title>

<script language="JavaScript">

var SecondsPerMinute = 60;
var MinutesPerHour = 60
var HoursPerDay = 24;

 var InputtedDays = prompt("How many days do you want to convert to seconds?","Enter number of days");

var SecondsPerInputtedDays = SecondsPerMinute*MinutesPerHour*HoursPerDay*InputtedDays;

</script>
</head>

<body bgcolor = "000044" text = "aaaaaa">

<H1>By my calculations</H1>
<font size = 4>
<script language="JavaScript">

var FirstPart = "There are ";
var MiddlePart = " seconds in ";
var LastPart = " days.";
 var WholeThing = FirstPart + SecondsPerInputtedDays + MiddlePart + InputtedDays + LastPart;

window.document.write(WholeThing);

</script>
</font>

</body>
</html>

 

Now, since we are adjusting to user input, the output becomes a little more complicated.  Assuming you put in a duration of 2.45 days like appears in the following prompt box

 

 

you should get a result that looks like the following.

 

 

Obviously, there are a lot of other uses for these.