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JavaScript Part 1
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JavaScript Simple scripting language => suitable for implementing simple tasks Tasks which run for short time Manipulation of the DOM of a Web page JavaScript is JUST ONE scripting language ( Perl, VBScript, Python, Tcl) Javascript has no relationship to Java
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JavaScript : Good & bad news
Widely supported in Web browsers Easy access to the DOM of Web pages No need for special plug-in to use the scripts Simple, easy to understand Secure since JavaScript can not read/write local hard drive DOM is not supported consistently Script does not work => Web page is useless Scripts can be slow and take long time to start up
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Including JavaScript in HTML
The tag <script> Attributes : Language Code enclosed as HTML comments <script language=“javascript”> <!-- JavaScript code --> </script>
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If there are many scripts (complex) then it is better to include the JavaScript source code in a separate file Re-usability <script language=“javascript” src=“sample.js”></script>
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JavaScript events JavaScript functions are activated by user events. (eventdriven programming). JavaScript => reactive to the user Examples: onChange onClick onFocus onLoad onMouseover onSelect onSubmit onUnload
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JavaScript event handlers
When an event happens then it is checked whether there is an appropriate event handler Event handler : JavaScript function If there is an event handler then the appropriate function is executed Event handlers are defined by associating events to Javascript functions <body onLoad=“mypage()”> <a href=“ onClick=“mylink()”>text</a>
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JavaScript syntax JavaScript is interpreted by the browser
comments : //some text statements are terminated with a semicolon code is enclosed in pairs of curly brackets arithmetic and logical operators as in Perl and C variables need to be declared before used automatic type conversion
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JavaScript variables in JavaScript you can define global or local variables variable names : consist of letter/digit/_ Case sensitive, no spaces, no reserved words data types : numeric, string, boolean var first = 23; var second = “some text”; var third = true;
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JavaScript program control
if (name == “John”) { do_something } else if (name == “Mike”) { do_something_else } }
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var I; for(I=1;I<10;I++) { do_something } while (I > 1) { I--; Note: we can use break and continue statements as C language
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JavaScript output // An example of creating HTML with JavaScript {
document.write(“<h1>Your details</h1>”); document.write(“<p>Your Name is :” + name); document.write(“<p>You Are” + age + “Years Old”); } notice that: there is no need to print the HTML header. the plus operator is used for embedding variables in HTML.
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JavaScript functions function name(parameter_list)
code in curly brackets. no return type. no parameters type. The return statement.
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// An example of a javascript function
function welcome() { var message = “Hello World!”; document.write(“<h1>” + message + “</h1>”); } <body onLoad=“welcome()”>
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Document Object Model All elements of Web page are accessible via the DOM. Document Object Model : A Web page is modelled as a hierarchy of objects Every HTML element is an object : paragraphs, images, tables, frames, lists, etc The DOM contains arrays for various elements i.e. forms, tables, form elements, etc Each element is accessed via a unique pathname within the DOM. Use the dot operator to traverse the document hierarchy (Similarities with UNIX and MSDOS)
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DOM (2) Root of the hierarchy : Document
Document.forms[0].elements[0].value Names of elements can also be used for the same purpose The DOM of a Web page is made available to scripts which can process it
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What are the DOM paths for each elements in the following slide?
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Hierarchy of objects of the previous slide
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What is going on here? <form name="myForm">
<input type="text" name="input" value="bla bla bla" size="20"> <input type="button" value="Write" onClick="document.myForm.input.value= 'Yo!'; "></form>
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The location-object Besides the window- and document-objects there is another important object: the location-object. This object represents the address of the loaded HTML-document. So if you loaded the page then location.href is equal to this address. What is more important is that you can assign new values to location.href. This button for example loads a new page into the actual window: <form> <input type=button value="Yahoo" onClick="location.href=’ "> </form>
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Two important built-in functions
parseInt : Takes a string as a parameter and returns it in integer format Example: num=parseInt(document.forms[0].text1.value); parseFloat : Takes a string as a parameter and returns a floating point representation of it num=parseFloat(document.forms[0].text1.value); IMPORTANCE : javascript makes the assumption that everything the user entered in a form is a string. Your program must transform strings into numbers if necessary
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Basic javascript windows
alert (“string”); confirm (“string”); (return true or false) prompt (“question”, “initial value”);
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Self Review Examples Read and practice with the following javascript examples
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Example: Events <html><script language="javascript"><!-- function a(num) { if (num==0) alert ("Event: onLoad"); else if (num==1) alert ("Event: onUnLoad"); else if (num==2 || num==4) alert ("Event: onChange"); else if (num==3) alert("Event: onSelect"); else if (num==5) alert("Event: onFocus"); else if (num==6) alert("Event: onClick"); else if (num==7) alert("Event: onSubmit"); } --></script> <body onLoad="a(0)" onUnLoad="a(1)"> <form onSubmit="a(7)"> <input type="text" onChange="a(2)" onSelect="a(3)"> <select onChange="a(4)"><option>Male</option><option>Female</option></select> <input type="button" onFocus="a(5)" onClick="a(6)"><input type="submit" value="Submit"> </form></body></html>
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Mouse Events Example <html><script language="javascript">
<!-- function a(index) { document.images[index].src="ball2.gif";} function b(index) { document.images[index].src="ball1.gif";} --></script> <body> <img border="0" src="ball1.gif" width="78" height="66" onMouseOut="b(0)" onMouseOver="a(0)"> <img border="0" src="ball1.gif" width="78" height="66" onMouseUp="b(1)" onMouseDown="a(1)"> </body></html>
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Example Write a simple Javascript function to verify the username and password typed by the user Assume there is only 1 valid combination : Username = Admin and Password = xyz If ok then print a thank you message else reset the form & alert the user of the error
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<html> <head> <script language=“javascript” src=“test.js”></script> </head> <body> <form> <input type=“text” name=“username” maxlength=“5”> <input type=“password” name=“pass” maxlength=“3”> <input type=“submit” value=“Login” onClick=“verify()”> </form> </body> </html>
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function verify() { var user=“admin”; var passcode=“xyz”; var username=document.forms[0].elements[0].value; var password=document.forms[0].elements[1].value; if (username == user) { if (password == passcode) { document.write(“<h1>Successful login</h1>”); } else { alert(“Sorry. Wrong Password”); document.forms[0].reset(); } else { alert(“Sorry. Wrong Username”);
![function verify() { var user= admin ; var passcode= xyz ; var username=document.forms[0].elements[0].value;](http://slideplayer.com./slide/7316631/24/images/32/function+verify%28%29+%7B+var+user%3D+admin+%3B+var+passcode%3D+xyz+%3B+var+username%3Ddocument.forms%5B0%5D.elements%5B0%5D.value%3B.jpg "var password=document.forms[0].elements[1].value; if (username == user) { if (password == passcode) { document.write( <h1>Successful login</h1> ); } else { alert( Sorry. Wrong Password ); document.forms[0].reset(); } else { alert( Sorry. Wrong Username );")
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Example The following example show how to extract data from various types of form elements.
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<html><body>
<p> </p> <form method="POST" action="" name="myForm"> <p>Name: <input type="text" name="T1" size="20"></p> <p>Interests: <textarea rows="2" name="S1" cols="20"></textarea></p> <p>Do you like? <input type="checkbox" name="C1" value="Newspapers">Newspapers <input type="checkbox" name="C2" value="Magazines"> Magazines</p> <p>Sex: <input type="radio" value="M" checked name="R1">Male <input type="radio" name="R1" value="F"> Female</p> <p>Country: <select size="1" name="D1"> <option value="Bahrain">Bahrain</option> <option value="Kuwait">Kuwait</option> <option value="Emirates">Emirates</option> <option value="Qatar">Qatar</option> <option value="other">Other</option> </select></p> <p><input type="button" value="Button" name="B1" onClick="extract()"></p></form>
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<script language="JavaScript"><!--
function extract() {var str=""; alert("Name : "+ document.myForm.T1.value + "\nInerests :"+ document.myForm.elements[1].value); if (document.myForm.C1.checked) str=document.forms[0].C1.value; if (document.myForm.C2.checked) str+=", " +document.forms[0].C2.value; alert("I like : "+ str); if (document.forms[0].R1[0].checked) alert("Sex :"+ document.forms[0].R1[0].value); else alert("Sex:"+document.forms[0].R1[1].value); alert ("Country :"+ document.myForm.D1.value); alert("Number of elements is " +document.forms[0].elements.length); str="R1 Radio buttons value are "; for (var i=0; i<document.forms[0].R1.length;++i) str+= document.forms[0].R1[i].value + ", "; str+=“ and Combo box options are: "; for (var i=0; i<document.forms[0].D1.length;++i) str+= document.forms[0].D1[i].value + ", "; alert (str); }--> </script> </body></html>
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