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Mobile Wireless Systems

Mobile Wireless Systems. Mobile Wireless Comms Lecture 7. JavaScript. JavaScript. Programming language for web browsers. Latest version is 1.8.1 (since 2009). Microsoft’s own version: JScript . Not 100% compatible with JavaScript.

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Mobile Wireless Systems

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  1. Mobile Wireless Systems Mobile Wireless Comms Lecture 7

  2. JavaScript

  3. JavaScript • Programming language for web browsers. Latest version is 1.8.1 (since 2009). • Microsoft’s own version: JScript. Not 100% compatible with JavaScript. • Is based on ECMA Script (specification ECMA-262 and ISO/IEC 16262), developed 1995. • Is object-oriented. Makes web pages highly interactive and dynamic. • References: http://www.w3schools.com/jsref/ http://www.javascriptkit.com/jsref/

  4. Use of JavaScript in HTML <script language="JavaScript“ type="text/javascript"> ... JavaScript code ... </script> • The <script> tag indicates scripting language. • Javascript needs to be enabled in the browser • Can be enabled by setting security to lower level.

  5. Enabling JavaScript in Web Browser • Set security settings to “Medium”. This will in general allow JavaScript to be executed. • In “Custom” security setting, find “enable scripting” and check this setting.

  6. Managing “JavaScript not enabled” If JavaScript is not enabled in browser: <noscript> <p>You need to enable JavaScript, otherwise this site will not work properly!</p> </noscript>

  7. Managing “JavaScript not enabled” • Several ways of handling missing JavaScript support: • Within one web page, provide alternative to scripting within the <noscript> tag pair. • If JavaScript is not supported by browser, then redirect to a page without JavaScript. • If JavaScript is supported by browser, then redirect to a page with JavaScript.

  8. Example: One Single Webpage <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <title>My first JavaScript Example</title> </head> <body> <script language="JavaScript" type="text/javascript"> var a = 1.234; </script> <noscript> You need to enable JavaScript, otherwise this site will not work properly! </noscript> This line is shown no matter if JavaScript is enabled or not.<br> <script language="JavaScript" type="text/javascript"> document.write("This is shown only when JavaScript is enabled<br>"); document.write(" <b>a = " + a + "</b>"); </script> </body> </html> File: http://creativetech.inn.leedsmet.ac.uk/MWC/JavaScript1.html

  9. Redirect if JavaScript Disabled <NOSCRIPT><meta http-equiv="refresh" content="2; URL = PageWithoutJavaScript.html">  </NOSCRIPT> • This method does not validate with w3 validator. http://creativetech.inn.leedsmet.ac.uk/MWC/RedirectIfNoJavaScript.html

  10. Redirect if JavaScript is Enabled <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN""http://www.w3.org/TR/html4/strict.dtd"> <html> <head> <title>javascript or no javascript</title> <script type="text/javascript"> <!— location.href="JavaScript1.html"; //--> </script> </head> <body> <div>This is the javascript disabled page</div> </body> </html> http://creativetech.inn.leedsmet.ac.uk/MWC/RedirectIfJavaScript.html

  11. JavaScript Functions • JavaScript provides a set of functions for doing specific tasks. • Also: users can write functions themselves. • Examples of built-in JavaScript function: • document.write(textstring): • Prints text or variables on the web page. • document.getElementById(idstring): • Gets HTML element (DIV or other) which is named by the attribute “id”. • alert(): • Outputs a message box.

  12. Example Usage Write text: document.write("hello, world"); Get an element of web page: var d = document.getElementById("tag1");

  13. Example of User-Defined Function function ShowRandomNumber() { var a = Math.random(); // shows a random number between 0 and 1 alert("random number: " + a); return a; } http://creativetech.inn.leedsmet.ac.uk/MWC/JavaScriptFunction.html

  14. Get Browser Information Special variables in JavaScript contain some important information: Detailed information sent in the HTTP request header by the client: navigator.userAgent; Simple name of the browser (is often incorrect): navigator.AppName; Example: http://creativetech.inn.leedsmet.ac.uk/MWC/

  15. Events • Since HTML 4, most HTML tags can capture “events”: • onload, onunload, • Mouse events: onclick, … • A JavaScript function can be assigned to each event that occurs. • http://www.w3schools.com/TAGS/ref_eventattributes.asp

  16. Examples for Event Capture • Action after the web page has loaded: <body onload="DoSomething()"> • Action after a button has clicked: <input type="Button" onclick="DoSomethingElse()"> • The functions need of course to be defined, otherwise no action is being done.

  17. Example: Modify Tag Attributes • http://creativetech.inn.leedsmet.ac.uk/MWC/JavaScriptAttributes.html function ChangeHeadingColor(color) { d = document.getElementById("heading"); d.style.backgroundColor = color; }

  18. Output by JavaScript Directly into web page: document.write("text to write"); In a dialog box: alert("text"); Into a pre-defined area in a HTML tag: document.getElementById("tag1").innerHTML = "text to write"; http://www.w3schools.com/dhtml/dhtml_javascript.asp

  19. JavaScript in Separate Files • Javascript content can be in separate files, which can be included: • Locally: <script src="js/geo.js" type="text/javascript" charset="utf-8"></script> • Remote: <script src="http://code.google.com/apis/gears/gears_init.js" type="text/javascript" charset="utf-8"></script> • Files can contain variables and functions to be used later in the HTML code.

  20. JavaScript from APIs • There are external Application Programming Interfaces (APIs) offered by many services, for example: • Google Maps http://code.google.com/apis/maps/documentation/javascript/ • Yahoo http://developer.yahoo.com/yui/ • jquery http://jquery.com/

  21. JavaScript and Validation • HTML validators only check HTML code and get confused by JavaScript. • If the following are within JavaScript text output: </b>, </p>, or any other end HTML tags, they are recognised by the validator, but the begin tags are not recognised. • You need to use the escape sequence “\/” to create “/” in text output. • http://www.htmlhelp.com/tools/validator/problems.html#script

  22. Validation in Expressions • Special characters “&”, “<“, “>” in mathematical expressions cause XHTML validation error: • Put within the script area the following, to exclude such expressions from XML parsing: <script ... > <![CDATA[ ... ]]> </script> • CDATA = non-parsed Character Data. Validators and parsers will ignore what is defined as CDATA.

  23. Limitations on Mobiles • Limited stack size: • This limits the level of how “deep” nesting can go. • Limited page size: • Can be 10 MB page size limit. Leeds Metropolitan University Faculty of Art, Environment and Technology

  24. Browser Compatibility Tests • HTML 5: • http://html5test.com/ • Web Standards Project: http://www.acidtests.org/ • ACID 3 test: • http://acid3.acidtests.org/ • Javascript Compatibility tests: • http://robertnyman.com/javascript/ Leeds Metropolitan University Faculty of Art, Environment and Technology

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