CIS 119 JavaScript Overview

• Discuss history of JavaScript
• Describe JavaScript capabilities
• Describe JavaScript limitations
• Discuss what Ajax is and why it is useful

• JavaScript was created at Netscape by Brendan Eich in 1995.
• JavaScript was originally named Mocha, and then LiveScript, before becoming JavaScript.
• JavaScript is NOT Java - although is shares some of the same syntax as Java.
• Java was a very popular buzzword at the time JavaScript got its common name, leading many to believe it was an attempt to capitalize on the popularity of Java.
• The standards version of JavaScript is named ECMAScript [ECMA = European Computer Manufacturers Association].
• Microsoft's version of JavaScript is named JScript.
• Adobe's Actionscript (found in Flash and Flex) is a relative which is derived from ECMAScript.
• The new HTML5 standard assumes a new standard version of JavaScript which extends and standardizes many browser features, and adds a number of new features and capabilities to the JavaScript language.
• ECMAScript 6 was a major update to language features made after a long period of relative stability
• The plan is to have frequent (annual) updates to the ECMAScript standard and name them with year numbers, so ECMAScript 6 is also ECMAScript 2015, ECMAScript 7 is also ECMAScript 2016, etc.
• ECMAScript 7 (2016) has only a small number of changes
• Browser differences used to make cross-browser JavaScript code more difficult than it is now. Increased standardization and available JavaScript libraries make that task easier now.
• Ajax is now used to request and update webpages with server data without having to reload the page, increasing responsiveness and potentially decreasing network traffic.
• Many JavaScript frameworks are available to add functionality, special effects, and make make cross-browser scripting easier.

• create dynamic pages on the fly
• enable "rollovers"
• create simple interactive "calculators"
• animate images
• create slideshows
• use cookies
• validate form data
• open new windows
• work with dates and times
• modify the contents of child windows and frames
• create nifty graphics effects such as expandable/collapsible sections of documents, fade-in/fade-out effects, etc.
• using Ajax, JavaScript can also be used to update web page content without having to reload a web page
• Relatively new feature: greatly improved control of audio and video content
• Relatively new feature: improved integration for Ajax communication through native JSON support
• Relatively new feature: ability to draw on a canvas element
• Relatively new feature: greatly expanded client-side storage capability using localStorage and sessionStorage
• Relatively new feature: access to browser geolocation features
• Relatively new feature: ability to create multithreaded applications for greater efficiency (not well supported yet)

• A script can't close windows it didn't open.
• A script can't read info from a window it didn't open.
• There is normally no explicit file access (either read or write) on the client machine.
• Restricted resources (such as files) can be accessed through ActiveX controls.
• There are some other ways to access files on the local machine, but they are not common yet and will not be covered in this course - they require extensions beyond basic JavaScript.
• Since your code is run by the user's web browser, it is dependent on the user's browser.
• There are slight JavaScript differences between browsers.
• A user can turn JavaScript off in their browser.