[MUSIC] Okay, welcome back. You've now spent a couple of weeks working on the fundamentals of creating web pages. And this week, we're gonna move on to the next stage, which is interactivity. To sort of introduce that, I'd like to sort of think a little bit about the kind of web pages you'd be creating. So, if you think about what happens when you load a web page, you're at your computer, this person on the left. And you're, for example, visiting the Coursera page. I'll represent by the Coursera logo, but this is the server that hosts the Coursera web page. What happens on the kind of page that we've been creating so far is that you type in the URL and send that request. And then the server finds the HTML page and the CSS, and any of the images, and sends it back to you. And that's the basic interaction we've been working on, send a request and a whole page gets sent back to you. And that's perfectly good and that's well represents what web pages were like in the mid 90s. But a modern web page is actually far more interactive than that. Once you've loaded a page like the Coursera webpage that you're on now, in fact, what happens is you spend less time interacting. You will click on a video to make it play and that the web page will respond by playing the video. Or similarly, you might sort of click on a tab and it'll show you more information. You might hover over something and it'll show you a tooltip. There's lots of sort of consulates of bits of activity that are interacting directly with the web page in the browser. So these things aren't, well most of them aren't sending requests back to the server and loading new pages. They're sort of changing and manipulating the page you've got. And that's the kind of interactivity I'd like to talk to you about today. And in particular, focus on sort of the kind of interactivity you do with mouse clicks. So sort of clicking on elements or possibly hovering over elements. So this kind of interactivity is enabled by a third language called JavaScript. So we've already looked at two of the main web languages. HTML, in the first module, CSS, In the second module. JavaScript is the third language. If HTML is for the structure of a web page, CSS is for the style of a webpage. Well, JavaScript is for interactivity. And actually we'll discover it's for many other things as we go throughout the courses. It's possibly the most complex of the three web languages, but for now we'll use it for interactivity. If you're new to programming, JavaScript is probably the hardest of the three languages to come, because it really is a full programming language. And I'll try to introduce things from the very beginning, compared to many other programming languages, it isn't so complex. But we've also included some links to further materials if you feel you need some extra reading or extra support for learning JavaScript. On the other hand, if you are an existing programmer, there are a few things I'd like to point out. So many of you might have started programming with a language called Java, have experience with Java. And if you're in that position, for one thing, I really want to stress is that JavaScript is not Java. Though the names are similar, actually they're very different languages. So JavaScript came out about the same time as Java. It was quite a, sort of an exciting new language and as a marketing spin. They sort of tried to align it with Java. And in fact, JavaScript isn't really the official name. The official name is ECMAScript. But why I'm stressing this is that actually, even though JavaScript has a very similar syntax to Java, it's actually a very different language. A lot of the principles of JavaScript, underlying them, are very different conceptually for how things work in Java. And in fact, to many other languages such as [INAUDIBLE], Ruby, Python, etc. So throughout this course, I'll point out a number of moments where, when we're doing something in JavaScript, which seems really, really strange to somebody with a background in Java or most other programming languages. But it's perfectly fine in JavaScript. So even if you're used to programming in another language, there is still quite a few things to learn. And I will try my best to highlight them wherever possible. So now we know what we need to do. In the next video, I'll start taking you through the very basics of writing some interactive JavaScript. [SOUND]
