1 00:00:02,270 --> 00:00:03,210 So let's get started 2 00:00:03,210 --> 00:00:05,210 with some Standard Libraries. 3 00:00:05,210 --> 00:00:09,130 And for that, I'm actually going to work with 4 00:00:09,130 --> 00:00:11,220 the HTTP library. 5 00:00:11,220 --> 00:00:15,140 That library will help us with spinning up a web server, 6 00:00:15,140 --> 00:00:17,420 and actually here in the docs of the library, 7 00:00:17,420 --> 00:00:21,160 we have some dummy code for doing that. 8 00:00:21,160 --> 00:00:23,680 So in the end, we're just going to replicate that code, 9 00:00:23,680 --> 00:00:26,970 but I'm going to explain what's happening here. 10 00:00:26,970 --> 00:00:30,920 Now we see one important difference to note right away 11 00:00:30,920 --> 00:00:33,040 and that's the import syntax. 12 00:00:33,040 --> 00:00:36,390 Now, I don't just mean the import from syntax, 13 00:00:36,390 --> 00:00:39,810 which differs from the const require import syntax 14 00:00:39,810 --> 00:00:41,460 we used throughout this course, 15 00:00:41,460 --> 00:00:45,300 but I also mean, from where we are importing. 16 00:00:45,300 --> 00:00:47,240 That's a URL. 17 00:00:47,240 --> 00:00:51,500 As you learned, Node does support the import from syntax. 18 00:00:51,500 --> 00:00:54,060 I do cover that in the modern JavaScript 19 00:00:54,060 --> 00:00:56,310 with Node core section. 20 00:00:56,310 --> 00:01:00,710 But what Node doesn't support, are URL imports. 21 00:01:00,710 --> 00:01:05,470 Where we don't import from a local file or a module, 22 00:01:05,470 --> 00:01:08,810 but where we instead point at a file on another server 23 00:01:08,810 --> 00:01:10,400 to import that file. 24 00:01:10,400 --> 00:01:13,003 And that's something Deno does. 25 00:01:13,003 --> 00:01:17,260 Deno wants you to use such imports. 26 00:01:17,260 --> 00:01:21,250 The idea with Deno is not that you download everything 27 00:01:21,250 --> 00:01:24,720 you're going to use in your project and store it locally, 28 00:01:24,720 --> 00:01:27,680 but then instead, you can import from any JavaScript 29 00:01:27,680 --> 00:01:30,410 or TypeScript file on any server 30 00:01:30,410 --> 00:01:34,433 and start using those exported features in your files. 31 00:01:35,590 --> 00:01:37,850 This is a core philosophy of Deno 32 00:01:37,850 --> 00:01:40,820 and that's, of course quite different to Node. 33 00:01:40,820 --> 00:01:44,480 So therefore, here, if we want to use this standard library, 34 00:01:44,480 --> 00:01:47,740 the HTTP library, and from that library, 35 00:01:47,740 --> 00:01:52,100 the serve function exported from the server.ts file, 36 00:01:52,100 --> 00:01:55,510 then we have to go into our app.ts file 37 00:01:55,510 --> 00:01:57,420 and add this code in here. 38 00:01:57,420 --> 00:01:58,950 And this will then do just that. 39 00:01:58,950 --> 00:02:03,200 It will import a function from this remote file, 40 00:02:03,200 --> 00:02:05,600 and of course you can only import what's exported 41 00:02:05,600 --> 00:02:08,240 if we dive into the server.ts file though, 42 00:02:08,240 --> 00:02:11,663 we see that if we search for serve, 43 00:02:17,830 --> 00:02:19,820 If we search long enough, at least 44 00:02:22,750 --> 00:02:25,670 we have the exported serve function here, 45 00:02:25,670 --> 00:02:27,440 because it's exported here, 46 00:02:27,440 --> 00:02:29,453 we can import it with this code. 47 00:02:30,490 --> 00:02:33,670 So, this is how we import and we don't need to download 48 00:02:33,670 --> 00:02:38,410 or NPM install this, it's also not built into Deno 49 00:02:38,410 --> 00:02:41,510 so it's also not like the file system module, 50 00:02:41,510 --> 00:02:43,020 which comes with Node. 51 00:02:43,020 --> 00:02:45,430 Instead, it simply sits on another server 52 00:02:45,430 --> 00:02:47,490 and this is how we import it. 53 00:02:47,490 --> 00:02:49,520 Now serve is then a function 54 00:02:49,520 --> 00:02:53,390 that allows us to spin up a HTTP server. 55 00:02:53,390 --> 00:02:56,520 And we spin up that server by calling serve, 56 00:02:56,520 --> 00:02:59,850 and then through serve, we pass an object to configure it 57 00:02:59,850 --> 00:03:01,890 and in this object, we can, for example, 58 00:03:01,890 --> 00:03:04,360 specify the port on which we wanna listen. 59 00:03:04,360 --> 00:03:07,890 And here for development, we could do this on port 3000. 60 00:03:07,890 --> 00:03:10,793 We do this with the port property in this object. 61 00:03:11,870 --> 00:03:14,020 Now server then returns a server, 62 00:03:14,020 --> 00:03:16,580 which we can store in a constant. 63 00:03:16,580 --> 00:03:18,120 And now this server, 64 00:03:18,120 --> 00:03:21,080 of course could have incoming requests. 65 00:03:21,080 --> 00:03:25,550 In Node.js, we would now specify a callback function 66 00:03:25,550 --> 00:03:28,050 that executes for every incoming request. 67 00:03:28,050 --> 00:03:32,560 Deno instead embraces modern JavaScript features 68 00:03:32,560 --> 00:03:35,070 for all its core capabilities, 69 00:03:35,070 --> 00:03:37,700 and the server is no exception. 70 00:03:37,700 --> 00:03:39,020 In this example, snippet, 71 00:03:39,020 --> 00:03:43,280 we see how we listen to incoming requests in Deno 72 00:03:43,280 --> 00:03:47,260 with this strange construct here. 73 00:03:47,260 --> 00:03:50,000 Now for await of, 74 00:03:50,000 --> 00:03:52,110 is a JavaScript feature, 75 00:03:52,110 --> 00:03:54,130 it's not Deno exclusive. 76 00:03:54,130 --> 00:03:58,810 Instead, it's a JavaScript feature called async iterable 77 00:03:58,810 --> 00:04:02,690 Server, is this so called asynchronous iterable, 78 00:04:02,690 --> 00:04:07,140 which simply means it's like an array full of promises 79 00:04:07,140 --> 00:04:09,770 and it's an infinite array basically. 80 00:04:09,770 --> 00:04:12,930 So this server generates new promises 81 00:04:12,930 --> 00:04:15,070 which we can await like this, 82 00:04:15,070 --> 00:04:16,580 and the new promise, 83 00:04:16,580 --> 00:04:18,480 which then resolves, is generated 84 00:04:18,480 --> 00:04:20,300 for every incoming request. 85 00:04:20,300 --> 00:04:23,990 That's what server does under the hood, the Deno server. 86 00:04:23,990 --> 00:04:27,410 And you could build this entirely with vanilla JavaScript 87 00:04:27,410 --> 00:04:31,033 async iterables are vanilla JavaScript. 88 00:04:31,970 --> 00:04:34,920 Attached, you'll find a link to the MDN documentation 89 00:04:34,920 --> 00:04:37,700 for async iterables, in case you're interested 90 00:04:37,700 --> 00:04:40,090 in learning a bit more about them. 91 00:04:40,090 --> 00:04:42,780 So, if I copy this code here, 92 00:04:42,780 --> 00:04:46,880 into my app.ts file, we'll execute this code 93 00:04:46,880 --> 00:04:48,990 for every incoming request. 94 00:04:48,990 --> 00:04:53,040 And this is just a Deno's way of sending back a response 95 00:04:53,040 --> 00:04:56,210 on the request object which is generated 96 00:04:56,210 --> 00:04:57,990 for every incoming request. 97 00:04:57,990 --> 00:05:00,190 We got a respond method, 98 00:05:00,190 --> 00:05:03,940 which wants an object, where we can specify a body 99 00:05:03,940 --> 00:05:07,560 for the response, which will be sent back by Deno. 100 00:05:07,560 --> 00:05:09,630 So this is how we listen to requests, 101 00:05:09,630 --> 00:05:13,700 then do whatever we wanna do, and then respond back. 102 00:05:13,700 --> 00:05:16,350 And one noteworthy thing here, 103 00:05:16,350 --> 00:05:21,250 is that we have await here, on the top level like this. 104 00:05:21,250 --> 00:05:24,870 This is not wrapped in any asynchronous function 105 00:05:24,870 --> 00:05:27,310 as you often needed in Avro code, 106 00:05:27,310 --> 00:05:32,220 instead Deno out of the box supports top level await. 107 00:05:32,220 --> 00:05:34,650 So that you can use the await keyword 108 00:05:34,650 --> 00:05:37,050 outside of asynchronous functions. 109 00:05:37,050 --> 00:05:39,440 In modern versions of Node.js, 110 00:05:39,440 --> 00:05:41,450 this is also supported though, 111 00:05:41,450 --> 00:05:43,563 so that's not really a key difference. 112 00:05:44,440 --> 00:05:47,790 Well, with that, if we save this, 113 00:05:47,790 --> 00:05:51,460 if I now run this file with Deno run app.ts, 114 00:05:51,460 --> 00:05:55,280 it compiles and it will ultimately crash, 115 00:05:55,280 --> 00:05:56,750 but before it crashes, 116 00:05:56,750 --> 00:05:59,540 you see it downloads a bunch of things. 117 00:05:59,540 --> 00:06:02,460 And that happens because of this import. 118 00:06:02,460 --> 00:06:05,460 Whenever you import from a URL like this, 119 00:06:05,460 --> 00:06:07,016 when you execute the code, 120 00:06:07,016 --> 00:06:10,120 Deno goes ahead and reaches out to that server 121 00:06:10,120 --> 00:06:11,880 and downloads that file 122 00:06:11,880 --> 00:06:14,640 and of course, also dependencies of that file. 123 00:06:14,640 --> 00:06:18,370 So, all other files which are imported by that file 124 00:06:18,370 --> 00:06:21,600 and it downloads those files to your local machine, 125 00:06:21,600 --> 00:06:23,700 and caches them locally. 126 00:06:23,700 --> 00:06:26,410 so that when you run the script thereafter, 127 00:06:26,410 --> 00:06:28,460 it doesn't have to re-download them 128 00:06:28,460 --> 00:06:30,840 simply to speed up execution time, 129 00:06:30,840 --> 00:06:34,690 and to make sure it doesn't exhaust all your bandwidth. 130 00:06:34,690 --> 00:06:38,200 With this approach, you can also develop on a plane, 131 00:06:38,200 --> 00:06:41,740 assuming that you did pre-download all the files 132 00:06:41,740 --> 00:06:42,993 you'll eventually need. 133 00:06:45,970 --> 00:06:48,870 Now, after it did all that, it crashes however, 134 00:06:48,870 --> 00:06:52,110 and it again crashes because of a permission error 135 00:06:52,110 --> 00:06:55,040 that network access was denied. 136 00:06:55,040 --> 00:06:57,170 And this makes sense because I mentioned 137 00:06:57,170 --> 00:07:00,400 that as part of Deno's permission model 138 00:07:00,400 --> 00:07:04,100 some things, like writing or reading to files, 139 00:07:04,100 --> 00:07:08,540 but also network requests are blocked by default. 140 00:07:08,540 --> 00:07:11,680 And of course here, we wanna open up a server 141 00:07:11,680 --> 00:07:14,170 that has something to do with the network, 142 00:07:14,170 --> 00:07:16,280 and therefore it's blocked. 143 00:07:16,280 --> 00:07:19,900 So, to make sure that this code works, 144 00:07:19,900 --> 00:07:23,440 I now have to run app.ts, 145 00:07:23,440 --> 00:07:25,840 with an extra permission flag 146 00:07:25,840 --> 00:07:28,430 but here it's now, not allow write, 147 00:07:28,430 --> 00:07:31,700 because I'm not trying to write to any file 148 00:07:31,700 --> 00:07:35,330 instead, it's allow net and that's the permission flag 149 00:07:35,330 --> 00:07:37,870 for granting network permissions. 150 00:07:37,870 --> 00:07:40,500 And if I now hit enter, this executes the file 151 00:07:40,500 --> 00:07:43,310 with those proper permissions, 152 00:07:43,310 --> 00:07:47,140 and therefor now, we can open up localhost 3000 153 00:07:47,140 --> 00:07:51,270 in the browser, and we see "Hello world there" 154 00:07:51,270 --> 00:07:53,990 which is the response we're sending back. 155 00:07:53,990 --> 00:07:57,010 And this is now also a process that keeps on running 156 00:07:57,010 --> 00:07:59,620 just like a Node server does, 157 00:07:59,620 --> 00:08:01,690 until we quit it with Ctrl + C, 158 00:08:01,690 --> 00:08:05,250 because of course it keeps on listening for requests. 159 00:08:05,250 --> 00:08:07,460 We don't want this process to finish, 160 00:08:07,460 --> 00:08:09,080 it should keep on listening, 161 00:08:09,080 --> 00:08:11,720 and that's just what it does. 162 00:08:11,720 --> 00:08:15,850 Now, just as before, to have that side by side comparison, 163 00:08:15,850 --> 00:08:20,410 let's see how we would spin up a similar server, with Node. 164 00:08:20,410 --> 00:08:22,420 For that I'm going to quit it here, 165 00:08:22,420 --> 00:08:24,850 and now again, going to write some Node code. 166 00:08:24,850 --> 00:08:26,620 Feel free to do this on your own first, 167 00:08:26,620 --> 00:08:28,233 we'll do it together thereafter.