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Semelhante a Javascript 2009
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Javascript 2009
- 1. JavaScript Used by many. Understood by few. Matthew Batchelder Lead Developer, Plymouth State University
- 23. Simple Alert Box <html> <head> <title>Example Message Box Page</title> <script type=“text/javascript”> alert(‘I like butter’); </script> </head> <body> … </body> </html>
- 24. Confirm Box Bound to an Event <html> <head> <title>Example Message Box Page</title> <script type="text/javascript"> function doLoad() { document.getElementById('sweet-link').addEventListener(‘click’, confirmClick, false); }//end doLoad function confirmClick() { return confirm(‘Are you sure you wish to go to that link?’); }//end confirmClick window.addEventListener(‘load’, doLoad, false); </script> </head> <body> <a id="sweet-link" href="http://borkweb.com">BorkWeb</a> </body> </html> example
- 28. WAIT!!!!!!!!!!!!! Things can actually be a bit easier. How much? Well most of the above.
- 29. WTF? jQuery. That’s what we use on campus. It is awesome.
- 32. Finding Elements With $ $(‘a’) $(‘.class’) $(‘#id’) $(‘.content div’) $(‘input[name=bork]’) $(‘input:first’) Here’s an example . Check out the selector syntax for more info.
- 38. The End. Resources: JS: The Good Parts , Slide Examples , jQuery , Image Sprites , Mega Man !
Notas do Editor
- Javascript isn’t held in very good esteem. People don’t feel like they need to learn it before they start using it…because it *looks* familiar. Looks familiar. Works differently. When people try to use it and it doesn’t work as expected, they hate it even more.
- All valid: JavaScript is forced upon the developer if programming on the web or a platform with embedded JS This is true. The DOM (Document Object Model) sucks. Luckily there are JS libraries that ease that pain. Once again, the fault of the DOM This is hard to avoid, though there are companies – like Google – that are exerting effort to make JS . Well…there are a number of mistakes…but there are good parts too that make it powerful.
- Global: No linker. All variables get tossed in a global namespace. Reliability and security problems. XSS +: In a strongly typed environment like Java, that’s hunky dory. In a weakly typed environment…well…it isn’t always obvious if you are going to add or concatenate. Semicolon: These aren’t required and JavaScript tries to insert them for you. How? When the compiler runs into an error, it backs up to a line feed and converts it to a semicolon. typeof: A useful tool as it tells what the type of something is. If you ask what the type of an Object is…it says it is an object. If you do the same for a Number, NULL, a Function, etc…Object. Arrays: Arrays are all just hash tables. Keys are turned into strings. This has a performance hit (though it makes things really easy) == and !=: Type coercion. False: Too many bottom values that are confusing and mean different things
- Luckily there is a === that would answer false to everything.