javascript

JavaScript

Bartosz Sakowicz

JavaScript - basics

JavaScript is used in millions of Web pages to improve the design, validate forms, detect browsers, create cookies, and much more.

JavaScript is the most popular scripting language on the internet, and works in all major browsers, such as Internet Explorer, Mozilla, Firefox, Netscape, Opera.

JavaScript – basics (2)

•JavaScript was designed to add interactivity to HTML pages

•JavaScript is a scripting language

•A JavaScript is usually embedded directly into HTML pages

•JavaScript is an interpreted language

•It is free

Java != JavaScript !!!

JavaScript - examples

<html>

<body>

<script type="text/javascript">

<!–

document.write(“It is JavaScript!")

//-->

</script>

</body>

</html>

JavaScript – examples(2)<html><head>

<script type=“text/javascript”>

function pushbutton() {

alert(“Hello!");

}

</script></head><body>

<form>

<input type="button" name="hello" value=“Hello" onclick="pushbutton()">

</form>

</body></html>

JavaScript – examples(3)<html><head>

<script type=“text/javascript”>

function getname(str) {

alert("Hi, "+ str+"!");

}

</script></head><body>

<p>Enter your name:</p>

<form>

<input type="text" name="name" onblur="getname(this.value)" value="">

</form></body></html>

Inserting JavaScript

1) <head> section (as in previous transparencies)

2) Inline scripts:

<body> <script type="text/javascript"> .... </script> </body>

3) External file:

<head>

<script src=“menu.js"></script>

</head>

Hierarchy of objects

Window Navigator

LinkAnchor

HistoryDocumentLocation

TextareaTextSubmitSelectResetRadioPasswordHiddenCheckboxButton

ImageForm

Basics usage of objects

a) With dot (.) – the same as in C++ (preferred way)

b) With usage the table of properties of object, eg:

document[1] – useful with loops

c) With usage of association table:

document["href"]

Expressions & operators

x=7; // variables doesn’t have type!

str = “Some text";

(bool1 == true) && (bool2 == false);

str = “Some" + " text";

All the operators are identical as in C++/Java.

Control flow statements

Statement Example usage

break for(i=1; i<5; i++) {// expressionsbreak; }

continue The same as break.

for See break..

for..in for (i in obj) {// expressions}

goto goto label1;

if..else if(condition) {// expressions if true } else {// expressions if false }

return function sum(a,b) {x=a+b; return x;}

while do-while

while(condition) {//expressions} do { //expressions } while (condition)

with with (document) {write " Some text "; }

Events - onload and onUnload

Events are triggered when the user enters or leaves the page.

The onload event is often used to check the visitor's browser type and browser version,

Events are often used to deal with cookies that should be set when a user enters or leaves a page.

Eg:

<body onload="DoSthonload">

<body onunload="DoSthonunload">

Events - onFocus, onBlur and onChange

Events are often used in combination with validation of form fields.

Eg:

<input type="text" size="30“

id="email" onchange="checkEmail()">;

Events - onSubmit

Event is used to validate all form fields before submitting it.

Eg:

<form method="post" action="xxx.htm"

onsubmit="return checkForm()">

Events - onMouseOver and onMouseOutEvents are often used to create "animated" buttons, eg:

<html><head>

<script type=“text/javascript”></script></head><body>

<a href= "doc.htm" onmouseover="changeImage(0,2)" onmouseout="changeImage(0,1)"> <img src=“image1.gif" alt=“image1"/></a>

<a href= "doc.htm" onmouseover="changeImage(1,2)" onmouseout="changeImage(1,1)"> <img src=“image1.gif" alt=“image1"/></a></body></html>

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