Javascript
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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.

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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>


<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(2)


<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>

JavaScript – examples(3)


Inserting JavaScript

  • <head> section (as in previous transparencies)

  • Inline scripts:

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

  • 3) External file:

  • <head>

  • <script src=“menu.js"></script>

  • </head>


Hierarchy of objects


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.


Statement

Example usage

break

for(i=1; i<5; i++) {

// expressions

break; }

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 ";}

Control flow statements


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 onMouseOut

Events are often used to create "animated" buttons, eg:

<html><head>

<script type=“text/javascript”><!--

function changeImage(i,j) {

document.images[i].src = “image"+j+".gif";

}--></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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