Lecture Summary 7
Prepared by: Anthony Larrain
Javascript Functions.
- A function typically takes one or more inputs and returns a single value. Some functions do not return values.
- Javascript provides many built in functions that perform various tasks. Such as
prompt("Enter name");
parseFloat("35.3");
document.write("Welcome");
Most functions return a value that we can use in our programs.
prompt returns the string we enter into the textbox.
parseFloat returns the string converted to a numeric value.
We can assign this value to a variable
name = prompt("Enter name");
temperature = parseFloat("35.3");
Javascript provides many functions to perform mathematical tasks.
To use these functions use the name Math followed by the dot '.' operator and the name of the function.
Example
To find the square root of a number we would write
Math.sqrt(16);
This function inputs 16 and returns 4, which we would normally assign to a variable.
result = Math.sqrt(16);
The Power Function
<![CDATA[
<html>
<!-- Example Javascript program for It130 -- Anthony Larrain -->
<head><title> Javascript Power Function Example</title></head>
<body>
<h3>Power Function Tester</h3>
<script type="text/javascript">
var base = prompt("Enter the base", "");
var exponent = prompt("Enter exponent", "");
var result = Math.pow(base, exponent);
document.write(base + "<sup>" + exponent + "</sup> = " + result);
</script>
</body>
</html>
]]>
power.html
Lotto Numbers
<![CDATA[
<html>
<!-- Example Javascript program for It130 -- Anthony Larrain -->
<head><title> Javascript Power Function Example</title></head>
<body>
<h2>Pick Four</h2>
<script type="text/javascript">
var num1 = Math.floor( 10 * Math.random() );
var num2 = Math.floor( 10 * Math.random() );
var num3 = Math.floor( 10 * Math.random() );
var num4 = Math.floor( 10 * Math.random() );
document.write("Your Lotto Numbers are .. " + num1 + " - " + num2 + " - " + num3 + " - " + num4);
</script>
</body>
</html>
]]>
lottery.html
Alert Window
- A Javascript function used to alert a visitor of your page to a message.
- The alert window is a dialog box, like prompt, except no textbox for input.
- Alerts are annoying to users and should be used sparingly.
alert1.html
alert2.html
In alert2 demo, the body tag has an attribute called onUnLoad. This attribute can be used to specify
code that is executed when the user leaves the page.
var first, second, result
first = 2;
second = 3
1) result = Math.pow(first, second);
2) result = Math.pow(first, second + second);
3) result = Math.pow(second, 2);
4) result = Math.pow(first + 1, second - 3);
5) result = 3 * Math.pow(first, 2);
6) result = 3 + Math.pow(first, 2);
7) result = 3 + Math.pow(first, 4) / 4;
8) result = Math.sqrt(16) + Math.pow(3, 2);