The recent introduction of MySQLi also provides more secure options for developers. This is a key component in building login systems and admin panels.
jQuery allows for the user to see content update live, without refreshing the page. This is how Facebook and Twitter posts work, you don't have to reload the page, the posts just appear. jQuery does this and it does it well.
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It's the reason you're reading this paragraph, because you clicked on the 'JS' tab, which ran some JavaScript code to switch to this paragraph. There's also several adaptations of JavaScript, which are nearly a new language in their own right, jQuery is one of these and works in a similar way to Ajax, to provide live, dynamic content.
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The above shows my web-related skills, the languages I can confidently write and create websites with. These languages allow me to achieve anything you see on other webpages, I've described the uses of each language briefly, if you're interested in how a website is stuck together.
If you're interested in having a website built for you, all the code I write will belong to you, the code can also be commented so that you can understand it or have other developers work.