1. 1 Server versus Client-Side Programming Server-SideClient-Side

2. What is JavaScript? 2

3. Embedding JavaScript in a Web Page 3 To place JavaScript in a Web page use the tag: script commands Each script command is a single line that indicates an action for the browser to take. Each command ends with a semi-colon. Place scripts anywhere. If placed in, it is immediately interpreted and run.

4. A Sample Command 4 To write text to a Web page with JavaScript, use the command: document.write(“text”); where text is the HTML code to be written to the Web page. document is an example of an object (a thing you manipulate) write is an example of a method (an action you perform on the object)

5. 5 Some JavaScript Syntax Rules JavaScript is case sensitive JavaScript ignores most occurrences of extra white space In general, do not break a statement into several lines The + symbol used in a command combines several text strings into a single text string, e.g. “Rick “ + “Bournique” is the same as “Rick Bournique”

6. JavaScript Variables 6 A variable is a named item in a program that stores a data value Variables should always be declared (reserve memory) but isn’t required by JavaScript To declare a JavaScript variable: var variable ; Example: var area, diameter; To declare a JavaScript variable and set its initial value: var variable = value; Example: var pi = 3.14159; Assignment: variable = value;

7. Types of JavaScript Variables 7 Numeric: any number, such as 13, 22.5, -77 Text: any group of text characters, such as “Hello” or ‘Happy Holidays!’ Must be enclosed within either double or single quotations (but not both) Boolean:only true and false Null: no value at all, e.g. x = null; JavaScript is a weakly typed language. This is OK: total = 5 + 4; // 9 total = “face” + “book”; // facebook

8. Creating a JavaScript Function 8 A function is a collection of commands that performs an action or returns a value. Good for reuse. General form: function function_name(parameters){ JavaScript commands return value; } Example: function CalculateArea(radius) { area = 3.14159 * radius * radius; return area; } Functions are not required to return values. Good practice to put all functions in

9. Calling a JavaScript Function 9 Once a function is created, you can call the function (i.e., run it). Example: function CalculateArea(radius) { area = 3.14159 * radius * radius; return area; } var r = 10; a = CalculateArea(r); document.write(a); Function is called with a parameter, r, of 10.

10. Placing JavaScript in an External File 10 To access an external JavaScript file: <script src="url" type="text/javascript "> where url is the URL of the external document

11. Inserting Comments in JavaScript 11 Commenting your code is an important practice

12. Debugging JavaScript 12 Debugging is the process of searching code to locate a source of trouble Three types of errors can occur: Load-Time Errors (also called compile-time or syntax) Example: area = 3.14159 * radius *radius Run-Time Errors Example: area = 3.14159 * Radius *Radius; Logical Errors Example: area = 13.14159 * radius *radius;

13. A Useful Debugging Tool: Alert Functions 13 The alert function in JavaScript displays a dialog box that shows a text message with an OK button url = “cadler@mpl.gov”; alert(url);