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Introduction. The scripting language most often used for client-side web development. Influenced...
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JAVASCRIPTIntroduction
OVERVIEW
The scripting language most often used for client-side web development.
Influenced by many programming languages, easier for nonprogrammers to work with.
Best known for its use in website development.
Unrelated to Java programming -- although both have a common C syntax
Supports all the structured programming syntax in C, Java, C#. – variables, conditionals, repetition structures, data structures, classes
USE IN WEBPAGES Primary use is to write function that are embedded
in HTML pages: Examples:
popping up a new window with control over size, position, attributes.
Validation of web form input values to make sure they are acceptable before submitting to server.
Changing images as a mouse moves over them.
The JavaScript interpreter interprets JavaScript source code and execute the script accordingly. not a compiled language like C or C++
Most common host environment for JavaScript is a web browser
OVERVIEW JavaScript is object based Client side scripting – runs on browser,
not on serverDon't need to send and retrieve data to the
serverSaves time
Does not need to be compiledScript interpretation done by browser
USING <SCRIPT> TAGS To tell html you will be using JavaScript do
this:
<script type=”text/javascript”> …. </script>
Everything between the opening and closing tags is JavaScript
Browser treats code as scripting language not html
Place <script> inside head tag, the browser interprets <head> first so the JavaScript will execute before the body
WHERE TO PUT <SCRIPT> If <script> placed in <head> tag, it gets
run first If <script> placed in <body> tag, runs in
order it was placed JavaScript can be placed in an external
file
<script type=”text/javascript” src=“myJavaScript.js” </script>
External JavaScript files end with .js extension
FIRST SCRIPT<script type="text/javascript">
document.write(“hello world!");
alert(‘hello world’);
</script>
“hello world” is a character string - a string of characters contained between double or single quotes
parentheses following the name of the method containing the arguments that the method requires to perform its task.
Every statement should end with a semicolon (not required but a programming standard).
JavaScript is case sensitive method write() – write a line of text
COMMENTS Good practice to comment your code –
explain what your code does Comments – ignored by the browser One line comment
// This is a one line comment Multi-line comment
/* this is a multi-line commentI have a lot to explain
*/
TRACKING DOWN ERRORS
In Chrome – JavaScript Debugger is F12 or CTRL, shift J
In Firefox, use the error console (CTRL, Shift, J) Provides clear description of errors Identifies the line in your code where error
occurred
TRY Fade in practice
chapter1 – 1.html
