1 00:00:01,110 --> 00:00:03,390 ‫So, in the previous lecture, we learned how 2 00:00:03,390 --> 00:00:06,930 ‫to handle fetching data using promise methods. 3 00:00:06,930 --> 00:00:09,420 ‫But in this lecture, let's take it one step further 4 00:00:09,420 --> 00:00:13,350 ‫and learn how to do the exact same thing with a much nicer 5 00:00:13,350 --> 00:00:16,053 ‫and cleaner syntax called async/await. 6 00:00:17,400 --> 00:00:21,295 ‫So, this syntax that we just learned here works really well 7 00:00:21,295 --> 00:00:26,040 ‫but it's not the most easy thing to work with, I would say. 8 00:00:26,040 --> 00:00:28,812 ‫It's not the most beautiful code, in a way. 9 00:00:28,812 --> 00:00:32,694 ‫And so, we can basically implement this logic here 10 00:00:32,694 --> 00:00:35,900 ‫in a different way using async functions 11 00:00:35,900 --> 00:00:38,370 ‫and the await keyword. 12 00:00:38,370 --> 00:00:41,100 ‫Now, everything I explained to you in the previous lecture 13 00:00:41,100 --> 00:00:44,490 ‫is still 100% valid, and the whole idea 14 00:00:44,490 --> 00:00:47,130 ‫behind promises doesn't go away. 15 00:00:47,130 --> 00:00:48,759 ‫The only thing that's going to go away 16 00:00:48,759 --> 00:00:52,320 ‫is these then handlers right here. 17 00:00:52,320 --> 00:00:56,523 ‫So, we're going to again, do it in a cleaner way. 18 00:00:58,470 --> 00:01:00,870 ‫So, now instead of just doing it like this, 19 00:01:00,870 --> 00:01:03,393 ‫let's create an async function. 20 00:01:04,290 --> 00:01:08,310 ‫So, that's simply a function with the async keyword and 21 00:01:08,310 --> 00:01:13,310 ‫before it, and then let's call it or get todos. 22 00:01:21,840 --> 00:01:24,722 ‫Then let's just grab this part here 23 00:01:24,722 --> 00:01:29,722 ‫and I will actually now comment all of this out here. 24 00:01:34,050 --> 00:01:39,050 ‫And so now we can, inside the async function, await this. 25 00:01:39,720 --> 00:01:42,780 ‫So, await this promise immediately right here. 26 00:01:42,780 --> 00:01:44,970 ‫And what will happen then is that actually, 27 00:01:44,970 --> 00:01:48,240 ‫inside this async function, JavaScript will not 28 00:01:48,240 --> 00:01:52,635 ‫immediately move on to the next line, like it usually does. 29 00:01:52,635 --> 00:01:55,744 ‫So, as I explained in the previous lecture, JavaScript, 30 00:01:55,744 --> 00:01:58,890 ‫by default, will always immediately move on 31 00:01:58,890 --> 00:02:00,000 ‫to the next line. 32 00:02:00,000 --> 00:02:03,660 ‫It never waits for anyone, basically. 33 00:02:03,660 --> 00:02:07,350 ‫So, here as we fetch, it'll then immediately move here, 34 00:02:07,350 --> 00:02:09,480 ‫move here, and move here. 35 00:02:09,480 --> 00:02:13,020 ‫It'll, of course, not execute these callback functions, 36 00:02:13,020 --> 00:02:15,870 ‫but it will basically register them. 37 00:02:15,870 --> 00:02:18,570 ‫That's not really important, but what is important is 38 00:02:18,570 --> 00:02:22,680 ‫that we saw that immediately, this code here was locked 39 00:02:22,680 --> 00:02:23,610 ‫to the console. 40 00:02:23,610 --> 00:02:27,660 ‫So, way before the data from the API actually arrived. 41 00:02:27,660 --> 00:02:31,282 ‫But now, with the await keyword inside the async functions, 42 00:02:31,282 --> 00:02:34,816 ‫for the first time in JavaScript, we do actually have a way 43 00:02:34,816 --> 00:02:39,323 ‫of stopping and of pausing the code inside a function. 44 00:02:39,323 --> 00:02:43,230 ‫And by doing this, it makes the function looks a lot more 45 00:02:43,230 --> 00:02:46,278 ‫normal again and a lot more like normal, 46 00:02:46,278 --> 00:02:48,363 ‫synchronous JavaScript code. 47 00:02:49,260 --> 00:02:53,220 ‫Because then we can very simply store the result 48 00:02:53,220 --> 00:02:55,773 ‫of this here into a variable. 49 00:02:57,930 --> 00:02:59,621 ‫So, let's again call it response 50 00:02:59,621 --> 00:03:02,820 ‫and it's the exact same name as before. 51 00:03:02,820 --> 00:03:05,250 ‫So, here we call the response a res 52 00:03:05,250 --> 00:03:09,540 ‫inside this callback function because, well, the response 53 00:03:09,540 --> 00:03:13,904 ‫of the fetch is the data that is passed into this callback. 54 00:03:13,904 --> 00:03:17,430 ‫So, basically the response is this res. 55 00:03:17,430 --> 00:03:21,378 ‫So here, we can immediately and directly call it like this 56 00:03:21,378 --> 00:03:24,630 ‫in a way that is a lot more legible 57 00:03:24,630 --> 00:03:27,033 ‫and a lot more easy to understand. 58 00:03:28,350 --> 00:03:30,350 ‫And the same thing, then, with the data. 59 00:03:32,670 --> 00:03:34,950 ‫So, we can immediately call it data 60 00:03:34,950 --> 00:03:39,900 ‫and then simply await res.jsn. 61 00:03:39,900 --> 00:03:44,900 ‫And then we can log it to the console just like this. 62 00:03:46,080 --> 00:03:49,203 ‫And then we can call that function out here. 63 00:03:53,280 --> 00:03:55,350 ‫And there we go. 64 00:03:55,350 --> 00:03:59,823 ‫So, here we get all this data that we had before again. 65 00:04:02,100 --> 00:04:04,860 ‫But, of course, that waiting only works 66 00:04:04,860 --> 00:04:06,810 ‫inside this async function. 67 00:04:06,810 --> 00:04:10,020 ‫So, if here we again logged Jonas to the console, 68 00:04:10,020 --> 00:04:12,300 ‫you would see that Jonas, of course, 69 00:04:12,300 --> 00:04:14,700 ‫needs to be logged again before. 70 00:04:14,700 --> 00:04:18,060 ‫Because while JavaScript here simply defines the function, 71 00:04:18,060 --> 00:04:21,060 ‫then it derives here, it calls the function 72 00:04:21,060 --> 00:04:24,270 ‫and immediately it moves on to the next line. 73 00:04:24,270 --> 00:04:27,180 ‫But this function here, while being executed, 74 00:04:27,180 --> 00:04:30,559 ‫does actually wait, but only here inside this async function 75 00:04:30,559 --> 00:04:34,473 ‫and only in the lines that have this await keyword. 76 00:04:35,490 --> 00:04:39,030 ‫So, what do you think would happen if we actually would try 77 00:04:39,030 --> 00:04:42,483 ‫to return something from here and store it into a variable? 78 00:04:44,160 --> 00:04:49,050 ‫So like, returning these posts? Well, that's not correct. 79 00:04:49,050 --> 00:04:52,113 ‫Well, actually, yeah, data. It's called data right here. 80 00:04:53,310 --> 00:04:56,880 ‫Now, let's try to store that here into some variable. 81 00:04:56,880 --> 00:04:59,703 ‫So, todos equal, get todos. 82 00:05:02,040 --> 00:05:03,930 ‫So, what do you think would be logged 83 00:05:03,930 --> 00:05:05,230 ‫to the console right here? 84 00:05:06,750 --> 00:05:09,884 ‫Well, we can see it here. It is a promise. 85 00:05:09,884 --> 00:05:12,720 ‫So, what's going on here? 86 00:05:12,720 --> 00:05:14,793 ‫Well, it's the same thing as before. 87 00:05:15,780 --> 00:05:17,790 ‫Right after this function is being called, 88 00:05:17,790 --> 00:05:20,640 ‫JavaScript immediately moves on to the next line. 89 00:05:20,640 --> 00:05:22,260 ‫It does not wait. 90 00:05:22,260 --> 00:05:24,963 ‫And so at this point here, JavaScript has no way 91 00:05:24,963 --> 00:05:28,680 ‫of knowing yet what these todos are going to be. 92 00:05:28,680 --> 00:05:31,296 ‫And so simply, todos is a promise, 93 00:05:31,296 --> 00:05:35,756 ‫which means that the result value of this async function 94 00:05:35,756 --> 00:05:38,760 ‫is always just a promise. 95 00:05:38,760 --> 00:05:42,480 ‫And this is a fundamental piece of knowledge that you need 96 00:05:42,480 --> 00:05:44,908 ‫to have in order to work with async functions 97 00:05:44,908 --> 00:05:49,908 ‫and with asynchronous data in general in JavaScript. 98 00:05:50,310 --> 00:05:53,144 ‫Because now, if you wanted to actually get these todos 99 00:05:53,144 --> 00:05:57,480 ‫out here, you would again have to use the then method 100 00:05:57,480 --> 00:05:59,370 ‫on here or you would have 101 00:05:59,370 --> 00:06:01,890 ‫to use another async/await function. 102 00:06:01,890 --> 00:06:04,770 ‫Now, you have another promise in your hands here 103 00:06:04,770 --> 00:06:06,090 ‫that you need to handle. 104 00:06:06,090 --> 00:06:09,583 ‫But, fortunately for us, in React, that's not very common 105 00:06:09,583 --> 00:06:13,753 ‫because usually what we want as soon as we receive some data 106 00:06:13,753 --> 00:06:15,949 ‫is to set the state. 107 00:06:15,949 --> 00:06:19,380 ‫So, that we would do immediately here in this async function 108 00:06:19,380 --> 00:06:23,160 ‫and then we wouldn't usually return anything here. 109 00:06:23,160 --> 00:06:26,280 ‫So, this was just again showing you the synchronous 110 00:06:26,280 --> 00:06:29,190 ‫and asynchronous nature of JavaScript. 111 00:06:29,190 --> 00:06:31,212 ‫So, if you want to understand this a bit better, 112 00:06:31,212 --> 00:06:35,117 ‫then you can go ahead and compare these two solutions here, 113 00:06:35,117 --> 00:06:37,323 ‫which achieve the exact same thing, 114 00:06:38,280 --> 00:06:42,450 ‫and see how they are different and how, at least 115 00:06:42,450 --> 00:06:45,600 ‫in my opinion, this one is a lot nicer 'cause it looks, 116 00:06:45,600 --> 00:06:47,373 ‫again, like a normal function, 117 00:06:48,330 --> 00:06:50,700 ‫while this one here does not really. 118 00:06:50,700 --> 00:06:53,580 ‫So, here you can easily store the result 119 00:06:53,580 --> 00:06:56,721 ‫of the awaited data immediately into some variables. 120 00:06:56,721 --> 00:06:59,679 ‫And yeah, then use them in a flow 121 00:06:59,679 --> 00:07:03,180 ‫that looks just like synchronous code. 122 00:07:03,180 --> 00:07:06,596 ‫Okay, and with this, we actually finish our review 123 00:07:06,596 --> 00:07:10,830 ‫of Essential JavaScript for React section. 124 00:07:10,830 --> 00:07:12,962 ‫So, hopefully this brought you up to speed 125 00:07:12,962 --> 00:07:16,950 ‫with all the JavaScript that you need to know to be able 126 00:07:16,950 --> 00:07:19,710 ‫to now successfully complete this course. 127 00:07:19,710 --> 00:07:23,040 ‫And so, now the time has actually come to really move 128 00:07:23,040 --> 00:07:27,423 ‫onto the actual complete and ultimate React course.