1 00:00:02,050 --> 00:00:08,810 Now the last thing we saw on the previous definition slide is that Javascript runs on a host environment, 2 00:00:08,860 --> 00:00:15,850 so that means a Javascript engine can be part or can be executed in different environments. 3 00:00:15,850 --> 00:00:18,600 The most well known environment is the browser, 4 00:00:18,650 --> 00:00:24,400 modern browsers have Javascript engines built in and they're therefore capable of executing Javascript 5 00:00:24,400 --> 00:00:28,180 code but you also can run Javascript in other environments, 6 00:00:28,180 --> 00:00:34,810 for example on the server side, so right on a computer without having a browser in between, so not inside 7 00:00:34,810 --> 00:00:40,430 of a browser but simply execute code like this on your machine. 8 00:00:40,480 --> 00:00:47,140 Now Javascript was invented to run in the browser, to make web sites more dynamic, to be able to change 9 00:00:47,200 --> 00:00:55,630 things on a web site without loading a new page you could say because Javascript is able to closely 10 00:00:55,630 --> 00:00:59,890 work together with the loaded HTML code, with CSS, 11 00:00:59,920 --> 00:01:07,450 you can also use Javascript to send background HTTP requests, so to send some behind the scenes requests 12 00:01:07,450 --> 00:01:14,230 and fetch data without reloading the page and much more and it will do all of that throughout the course. 13 00:01:14,230 --> 00:01:19,310 Now there also are certain things Javascript can't do when it runs in the browser environment though, 14 00:01:19,420 --> 00:01:25,570 for example it can't access your local file system for security reasons because otherwise every web 15 00:01:25,570 --> 00:01:32,590 page you visit would be able to read your file system, maybe delete files on your computer and so on which 16 00:01:32,590 --> 00:01:34,120 would be horrible of course 17 00:01:34,390 --> 00:01:37,570 and in general it is running in a sandbox 18 00:01:37,600 --> 00:01:42,760 you can say, it's not able to interact with your operating system and so on, the browser gives you certain 19 00:01:42,760 --> 00:01:47,210 things you can do in this environment and doesn't allow other things. 20 00:01:47,230 --> 00:01:52,180 Now as I said, the browser is only one environment though, the one for which Javascript was invented 21 00:01:52,360 --> 00:01:55,880 but not the only one we're restricted to right now, 22 00:01:55,960 --> 00:02:04,960 instead the Javascript engine Google developed, v8 is the name of the engine, was extracted by some people 23 00:02:05,830 --> 00:02:11,290 to run Javascript anywhere because the idea was if we have the engine in the browser, why don't 24 00:02:11,290 --> 00:02:18,550 we take it out of the browser and then make it available as a standalone tool which you can use to execute 25 00:02:18,550 --> 00:02:21,400 Javascript anywhere else directly on your machine 26 00:02:21,400 --> 00:02:24,240 and this tool is in the end called Node.js. 27 00:02:24,410 --> 00:02:29,800 Now in this course, I'll have a separate module about Node.js where I show you how that works and 28 00:02:29,800 --> 00:02:35,080 how it uses the same Javascript syntax you learned throughout the course but which new features it 29 00:02:35,080 --> 00:02:40,420 brings to the table. For the majority of course however, we'll focus on the browser side because this is 30 00:02:40,420 --> 00:02:43,900 the side where you absolutely need Javascript 31 00:02:43,960 --> 00:02:48,670 and it's also the site where you're able to see more because you have a web page where things change 32 00:02:48,670 --> 00:02:49,870 and so on. 33 00:02:49,870 --> 00:02:55,030 Now back to Node.js though for a second, Node.js can be executed on any machine and therefore it's 34 00:02:55,090 --> 00:03:00,450 also often used to build web back-ends, to build web servers, server side 35 00:03:00,460 --> 00:03:04,490 Javascript is also something you often hear as a description for that. 36 00:03:04,570 --> 00:03:11,830 Now you might know about server side languages like PHP or also Java and other languages as well, 37 00:03:11,830 --> 00:03:17,450 well Javascript with Node.js can also be used to run it on the back-end of a web page, 38 00:03:17,470 --> 00:03:25,180 so on the server and not on the client in the browser of your users. Now Node.js also has certain things 39 00:03:25,180 --> 00:03:30,520 it can do and can't do, since it runs directly on a machine, in Node.js 40 00:03:30,540 --> 00:03:36,700 you're able to access the local file system, so you are able to write files and so on because unlike browser 41 00:03:36,700 --> 00:03:41,110 side Javascript, Node.js code has to be executed actively by you, 42 00:03:41,140 --> 00:03:44,280 it's not like you visit a web page and then this starts happening, 43 00:03:44,320 --> 00:03:47,890 instead it can only access the file system on the machine where it executes 44 00:03:47,890 --> 00:03:53,920 which for example is the server where it runs, not your machine and it's also able to interact with the 45 00:03:53,920 --> 00:03:55,390 operating system and so on. 46 00:03:55,390 --> 00:04:00,430 However on the other hand since it doesn't have direct access to the loaded web page, it can't manipulate 47 00:04:00,490 --> 00:04:02,970 HTML or CSS like browser side. 48 00:04:02,980 --> 00:04:10,530 Javascript is able to do, so we basically have even inverse access capabilities here and these are the 49 00:04:10,530 --> 00:04:13,080 different environments where Javascript is able to run. 50 00:04:13,090 --> 00:04:18,400 Now in this course, we'll focus on the browser side because the Javascript syntax you learned will be the 51 00:04:18,400 --> 00:04:22,030 same, no matter in which environment you run Javascript code 52 00:04:22,360 --> 00:04:27,540 but in the browser, we simply have more visual feedback and can see what happens. 53 00:04:27,670 --> 00:04:32,810 Nonetheless as I said, we have the separate Node.js module later in the course 54 00:04:32,830 --> 00:04:38,620 where I'll also dive into the different things we can do in Node.js and how that works.