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These are the user uploaded subtitles that are being translated: 1 1 00:00:01,360 --> 00:00:03,024 All right. 2 2 00:00:03,024 --> 00:00:05,460 So let's now implement the same sticky navigation 3 3 00:00:05,460 --> 00:00:07,980 that we implemented in the last video, 4 4 00:00:07,980 --> 00:00:12,063 but this time, using the new intersection observer API. 5 5 00:00:13,670 --> 00:00:17,990 But what actually is the intersection observer API, 6 6 00:00:17,990 --> 00:00:19,733 and why is it so helpful? 7 7 00:00:21,383 --> 00:00:23,990 Well, this API allows our code to basically 8 8 00:00:23,990 --> 00:00:28,400 observe changes to the way that a certain target element 9 9 00:00:28,400 --> 00:00:31,410 intersects another element, or the way 10 10 00:00:31,410 --> 00:00:33,413 it intersects the viewport. 11 11 00:00:34,579 --> 00:00:36,260 And so from this definition alone, 12 12 00:00:36,260 --> 00:00:38,580 I think you can see that this will actually 13 13 00:00:38,580 --> 00:00:42,223 be useful in implementing our sticky navigation. 14 14 00:00:43,378 --> 00:00:45,050 But let's actually start this video by learning 15 15 00:00:45,050 --> 00:00:49,200 how the intersection observer API actually works, 16 16 00:00:49,200 --> 00:00:51,560 but without our sticky navigation, 17 17 00:00:51,560 --> 00:00:54,160 because at the beginning, this can seem 18 18 00:00:54,160 --> 00:00:58,600 a bit intimidating and confusing, okay? 19 19 00:00:58,600 --> 00:01:02,250 So to use the intersection observer API, 20 20 00:01:02,250 --> 00:01:06,483 we need to start by creating a new intersection observer. 21 21 00:01:07,950 --> 00:01:12,823 So that's IntersectionObserver, just like this, 22 22 00:01:14,368 --> 00:01:16,880 and then here, we will have to pass in a callback function 23 23 00:01:16,880 --> 00:01:18,963 and an object of options. 24 24 00:01:20,110 --> 00:01:22,933 But let's leave that for a bit later, okay? 25 25 00:01:25,240 --> 00:01:27,650 So let's first store the result of calling this function 26 26 00:01:27,650 --> 00:01:29,043 into a new variable. 27 27 00:01:30,914 --> 00:01:33,470 So let's simply call it the observer, 28 28 00:01:33,470 --> 00:01:36,660 and so now, we have to use this observer 29 29 00:01:39,059 --> 00:01:40,959 to basically observe a certain target. 30 30 00:01:42,299 --> 00:01:46,503 So observer and then the method we call on that is observe. 31 31 00:01:48,228 --> 00:01:49,470 And then here, the target element. 32 32 00:01:49,470 --> 00:01:51,483 And this one will be section one, 33 33 00:01:52,810 --> 00:01:56,993 and so this is an element that we already selected before. 34 34 00:01:58,724 --> 00:01:59,660 So this will make a bit more sense 35 35 00:01:59,660 --> 00:02:03,360 once we actually create the callback and the options here, 36 36 00:02:03,360 --> 00:02:04,913 and let's start by the options. 37 37 00:02:08,946 --> 00:02:12,420 So const, let's call it the observer options, 38 38 00:02:12,420 --> 00:02:13,253 so obsOptions, 39 39 00:02:17,103 --> 00:02:18,430 so this is gonna be an object, 40 40 00:02:18,430 --> 00:02:21,193 and we can also already create the callback function. 41 41 00:02:22,589 --> 00:02:24,603 Let's simply call this observerCallback. 42 42 00:02:29,682 --> 00:02:31,600 All right, and of course, we could've created 43 43 00:02:31,600 --> 00:02:35,010 these right here, because this is where we will now 44 44 00:02:35,010 --> 00:02:38,540 pass them in, so first the callback, 45 45 00:02:38,540 --> 00:02:42,453 and second the options, okay? 46 46 00:02:43,685 --> 00:02:46,490 And so once again, we could've written the function 47 47 00:02:46,490 --> 00:02:48,930 and the object directly in here, 48 48 00:02:48,930 --> 00:02:52,043 but I think it's a bit cleaner to have them separately. 49 49 00:02:53,622 --> 00:02:55,672 So let's now start with the options here, 50 50 00:02:56,551 --> 00:02:59,860 and so this object needs first a root property. 51 51 00:02:59,860 --> 00:03:02,160 And this root is the element 52 52 00:03:02,160 --> 00:03:04,920 that the target is intersecting. 53 53 00:03:04,920 --> 00:03:07,650 So again, this here is the target, 54 54 00:03:07,650 --> 00:03:09,890 and the root element will be the element 55 55 00:03:09,890 --> 00:03:12,993 that we want our target element to intersect. 56 56 00:03:14,337 --> 00:03:15,720 And again, this will all make more sense 57 57 00:03:15,720 --> 00:03:17,393 once you see this in action. 58 58 00:03:18,560 --> 00:03:20,770 So we could now here select an element 59 59 00:03:20,770 --> 00:03:23,823 or as an alternative, we can write null, 60 60 00:03:24,905 --> 00:03:27,660 and then we will be able to observe our target element 61 61 00:03:27,660 --> 00:03:31,077 intersecting the entire viewport, all right?. 62 62 00:03:32,092 --> 00:03:34,570 So basically, this entire rectangle here, 63 63 00:03:34,570 --> 00:03:38,820 which shows the current portion of the page, okay? 64 64 00:03:38,820 --> 00:03:41,743 And then second, we can define a threshold. 65 65 00:03:43,990 --> 00:03:47,130 Threshold, and this is basically the percentage 66 66 00:03:47,130 --> 00:03:49,951 of intersection at which 67 67 00:03:49,951 --> 00:03:51,850 the observer callback will be called, 68 68 00:03:51,850 --> 00:03:53,133 so this callback here. 69 69 00:03:54,040 --> 00:03:55,780 So again that's very confusing, 70 70 00:03:55,780 --> 00:03:59,310 let's just set it to 10%, which is 0.1, 71 71 00:04:00,160 --> 00:04:02,530 and then when we have this callback function here 72 72 00:04:02,530 --> 00:04:06,822 also created, then we will see what actually 73 73 00:04:06,822 --> 00:04:08,870 happens here in practice. 74 74 00:04:08,870 --> 00:04:09,703 All right. 75 75 00:04:11,310 --> 00:04:13,940 So this callback function here will get called 76 76 00:04:13,940 --> 00:04:17,020 each time that the observed element, 77 77 00:04:17,020 --> 00:04:20,110 so our target element here, is intersecting 78 78 00:04:20,110 --> 00:04:25,110 the root element at the threshold that we defined, okay? 79 79 00:04:25,390 --> 00:04:28,380 So take note of this because this is actually 80 80 00:04:28,380 --> 00:04:31,563 a bit hard to figure out from reading the documentation. 81 81 00:04:32,961 --> 00:04:34,640 And so it's a good idea to keep note 82 82 00:04:34,640 --> 00:04:35,933 of what I'm saying here. 83 83 00:04:37,245 --> 00:04:40,140 So in the current example, whenever the first section, 84 84 00:04:40,140 --> 00:04:45,000 so our target here, is intersecting the viewport at 10%, 85 85 00:04:45,000 --> 00:04:48,012 so the viewport, because that's the root, 86 86 00:04:48,012 --> 00:04:50,263 and 10% because that's the threshold. 87 87 00:04:51,628 --> 00:04:53,950 So whenever that happens, then this function here 88 88 00:04:53,950 --> 00:04:57,230 will get called and that's no matter if we are scrolling 89 89 00:04:57,230 --> 00:04:59,833 up or down, all right? 90 90 00:05:00,690 --> 00:05:03,703 And this function will get called with two arguments, 91 91 00:05:04,805 --> 00:05:06,383 and so we can specify them here, 92 92 00:05:07,684 --> 00:05:11,363 and that's the entries and the observer object itself. 93 93 00:05:12,560 --> 00:05:15,160 All right, so this object here basically 94 94 00:05:15,160 --> 00:05:20,120 will also get passed into the callback function, all right? 95 95 00:05:20,120 --> 00:05:23,200 Now this case, we're only interested in the entries, 96 96 00:05:23,200 --> 00:05:26,990 but sometimes using the observer is also useful. 97 97 00:05:26,990 --> 00:05:30,090 Now we can have actually multiple thresholds, 98 98 00:05:30,090 --> 00:05:32,700 so here we can have an array, and I will do that 99 99 00:05:32,700 --> 00:05:35,550 in a minute, and so these entries here 100 100 00:05:35,550 --> 00:05:39,730 are actually an array of the threshold entries, okay, 101 101 00:05:39,730 --> 00:05:43,610 and so in this case again, there's only one element there, 102 102 00:05:43,610 --> 00:05:46,410 but let's create a more general function already 103 103 00:05:46,410 --> 00:05:48,970 which basically loops over these entries 104 104 00:05:50,550 --> 00:05:52,903 so that we can take a look at all of them. 105 105 00:05:54,749 --> 00:05:58,134 And so let's just do that, so basically, 106 106 00:05:58,134 --> 00:05:59,210 simply log them to the console, 107 107 00:05:59,210 --> 00:06:02,010 and that will already be good enough for us 108 108 00:06:02,010 --> 00:06:04,473 to take a look at how this all works. 109 109 00:06:07,371 --> 00:06:10,493 So entry, and so you see I'm using an arrow function here, 110 110 00:06:11,781 --> 00:06:14,681 but of course any other function would work just the same. 111 111 00:06:16,800 --> 00:06:18,950 Let's give it a save now, and you see that already, 112 112 00:06:18,950 --> 00:06:21,823 we get an intersection observer entry, 113 113 00:06:23,139 --> 00:06:24,689 and so that is this entry here. 114 114 00:06:26,790 --> 00:06:28,720 And so this is not really interesting yet, 115 115 00:06:28,720 --> 00:06:31,720 because this is just the first one that we got 116 116 00:06:31,720 --> 00:06:35,260 and we see that the ratio here is at zero, 117 117 00:06:35,260 --> 00:06:37,810 but let's see in a second what that actually means. 118 118 00:06:38,943 --> 00:06:40,450 So I will start scrolling here, and you see 119 119 00:06:40,450 --> 00:06:44,800 that now we actually got our first real entry here, 120 120 00:06:44,800 --> 00:06:47,740 which appeared here because our target element 121 121 00:06:47,740 --> 00:06:49,253 came into the viewport. 122 122 00:06:50,801 --> 00:06:53,428 So our target element is this whole h1 123 123 00:06:53,428 --> 00:06:56,654 that's down here, and so you see that it started 124 124 00:06:56,654 --> 00:06:58,667 intersecting the viewport, okay? 125 125 00:07:00,091 --> 00:07:02,230 And so our observer is observing that, 126 126 00:07:03,540 --> 00:07:06,630 and so now here you see that the intersection ratio 127 127 00:07:07,549 --> 00:07:10,250 at the time that this callback here was called, 128 128 00:07:10,250 --> 00:07:15,020 so this one here, was at 0.10, and then this. 129 129 00:07:15,020 --> 00:07:17,880 And so that's exactly the 10% threshold 130 130 00:07:17,880 --> 00:07:21,290 that we defined over here, all right? 131 131 00:07:21,290 --> 00:07:24,293 We also get this isIntersecting property, 132 132 00:07:25,279 --> 00:07:29,100 which in this case is true, and that is because indeed, 133 133 00:07:29,100 --> 00:07:32,270 our target, so again this whole section here, 134 134 00:07:32,270 --> 00:07:35,380 is now intersecting the viewport. 135 135 00:07:35,380 --> 00:07:38,400 And we are looking for the viewport, remember, 136 136 00:07:38,400 --> 00:07:40,623 because we set the root to null. 137 137 00:07:42,776 --> 00:07:43,609 All right? 138 138 00:07:45,346 --> 00:07:47,440 So we also get the target itself here, 139 139 00:07:47,440 --> 00:07:49,200 and a couple of other stuff, 140 140 00:07:49,200 --> 00:07:51,960 but the intersection ratio is actually 141 141 00:07:51,960 --> 00:07:55,883 the most interesting one and also the isIntersecting here. 142 142 00:07:57,665 --> 00:08:00,293 Okay, so let's scroll down a little bit more, 143 143 00:08:00,293 --> 00:08:02,230 and let's close this actually, 144 144 00:08:02,230 --> 00:08:05,280 and let's scroll up again, and so again, 145 145 00:08:05,280 --> 00:08:07,650 we get a new entry here, and so again, 146 146 00:08:07,650 --> 00:08:10,420 it should be close to 10%, 147 147 00:08:10,420 --> 00:08:14,030 but now it happened as we were moving up, right? 148 148 00:08:14,030 --> 00:08:16,970 And so again it was at 10%, but now, 149 149 00:08:16,970 --> 00:08:19,543 it is no longer intersecting, okay? 150 150 00:08:20,564 --> 00:08:23,653 And it's not intersecting because the threshold is at 10. 151 151 00:08:24,811 --> 00:08:28,480 And so now less than 10% basically of our target here 152 152 00:08:28,480 --> 00:08:32,700 are inside of the root, so inside of the viewport. 153 153 00:08:32,700 --> 00:08:35,230 All right, and so you can start to see 154 154 00:08:35,230 --> 00:08:37,580 why this is more efficient. 155 155 00:08:37,580 --> 00:08:41,240 So it's because we only get this kind of event here 156 156 00:08:41,240 --> 00:08:44,420 in the situation that we're actually interested in. 157 157 00:08:44,420 --> 00:08:48,713 So in this case, that's this threshold of 10%. 158 158 00:08:50,296 --> 00:08:51,650 Okay, and as we keep scrolling here, 159 159 00:08:51,650 --> 00:08:53,580 now it will come back again, 160 160 00:08:53,580 --> 00:08:56,173 and now it is again intersecting, 161 161 00:08:57,893 --> 00:09:00,680 let's keep scrolling, and all of this here is section one, 162 162 00:09:00,680 --> 00:09:02,253 and now we got another one. 163 163 00:09:03,922 --> 00:09:07,860 So let's see, and so now it is back to not intersecting, 164 164 00:09:07,860 --> 00:09:12,350 because now we no longer have 10% visible, okay? 165 165 00:09:12,350 --> 00:09:14,930 So you can think of this threshold here 166 166 00:09:14,930 --> 00:09:18,973 at the percentage that we want to have visible in our root. 167 167 00:09:20,107 --> 00:09:21,630 So in our viewport in this case, and so, 168 168 00:09:21,630 --> 00:09:24,850 right now we are back to having less than 10%, 169 169 00:09:24,850 --> 00:09:28,373 and so it is no longer intersecting here. 170 170 00:09:29,987 --> 00:09:32,260 And again, if we scroll up a little bit more, 171 171 00:09:32,260 --> 00:09:35,540 then we get another event here because now 172 172 00:09:35,540 --> 00:09:40,540 we are back to having 10% intersection ratio, okay? 173 173 00:09:41,100 --> 00:09:43,880 So this is the very fundamentals of how 174 174 00:09:43,880 --> 00:09:46,910 the intersection observer API works, 175 175 00:09:46,910 --> 00:09:50,500 and I confess that it is a bit confusing 176 176 00:09:50,500 --> 00:09:53,810 and it took me quite some time to figure all of this out, 177 177 00:09:53,810 --> 00:09:56,510 and so probably the best idea is for you 178 178 00:09:56,510 --> 00:09:58,720 to stop this video now and explore this 179 179 00:09:58,720 --> 00:09:59,970 a little bit on your own. 180 180 00:10:01,182 --> 00:10:03,972 So you can use different threshold values, 181 181 00:10:03,972 --> 00:10:05,822 and maybe use different targets here, 182 182 00:10:06,830 --> 00:10:08,220 you can even use different roots, 183 183 00:10:08,220 --> 00:10:10,840 and so it would be a good idea to experiment 184 184 00:10:10,840 --> 00:10:13,260 a little bit more with this. 185 185 00:10:13,260 --> 00:10:17,313 Now what I'm gonna do here is to now specify an array, 186 186 00:10:18,837 --> 00:10:20,660 so to specify different thresholds, 187 187 00:10:20,660 --> 00:10:22,490 and one of them is gonna be zero, 188 188 00:10:22,490 --> 00:10:26,543 and the other one 0.2, so that's 20%. 189 189 00:10:27,822 --> 00:10:30,510 So 0% here means that basically our callback 190 190 00:10:30,510 --> 00:10:33,740 will trigger each time that the target element 191 191 00:10:33,740 --> 00:10:36,223 moves completely out of the view, 192 192 00:10:37,377 --> 00:10:40,073 and also as soon as it enters the view, okay? 193 193 00:10:41,358 --> 00:10:42,450 And so that's because the callback function 194 194 00:10:42,450 --> 00:10:44,960 will be called when the threshold is passed 195 195 00:10:44,960 --> 00:10:48,313 when moving into the view and when moving out of the view, 196 196 00:10:49,477 --> 00:10:52,000 and this is really important to remember here. 197 197 00:10:52,000 --> 00:10:55,100 On the other hand, if we specified one here, 198 198 00:10:55,100 --> 00:10:57,770 like this, then that means that the callback 199 199 00:10:57,770 --> 00:11:01,500 will only be called when 100% of the target 200 200 00:11:01,500 --> 00:11:03,853 is actually visible in the viewport. 201 201 00:11:05,010 --> 00:11:06,253 So in the case of this section one, 202 202 00:11:06,253 --> 00:11:10,320 that would be impossible because the section itself 203 203 00:11:10,320 --> 00:11:12,233 is already bigger than the viewport. 204 204 00:11:13,756 --> 00:11:16,530 But let's now experiment with zero here, 205 205 00:11:16,530 --> 00:11:20,820 and so right away, we again get this event here, 206 206 00:11:20,820 --> 00:11:22,790 and you see that the intersection ratio 207 207 00:11:22,790 --> 00:11:26,740 is exactly at zero, but it is already intersecting, 208 208 00:11:26,740 --> 00:11:30,060 and so it's because basically the threshold here 209 209 00:11:30,060 --> 00:11:31,463 was already passed. 210 210 00:11:33,630 --> 00:11:35,190 All right? 211 211 00:11:35,190 --> 00:11:37,090 So I think another one happened there, 212 212 00:11:38,002 --> 00:11:41,050 let's just reload, oh, and that was probably 213 213 00:11:41,050 --> 00:11:42,933 from our 20%. 214 214 00:11:44,700 --> 00:11:47,525 Yep, so you see, this is the 20 threshold, 215 215 00:11:47,525 --> 00:11:48,570 the one that we set here now, 216 216 00:11:48,570 --> 00:11:51,900 and so this one now happened a little bit later than before, 217 217 00:11:51,900 --> 00:11:54,470 because before, it was happening at 10%, 218 218 00:11:54,470 --> 00:11:56,490 but now only at 20%. 219 219 00:11:56,490 --> 00:11:57,683 So that's a bit later. 220 220 00:11:59,224 --> 00:12:01,173 Let's just clear this and keep scrolling, 221 221 00:12:02,140 --> 00:12:04,993 and so now this section is almost scrolling out of view, 222 222 00:12:06,533 --> 00:12:09,063 and you see, we now get this 20% here. 223 223 00:12:10,368 --> 00:12:14,070 So a bit less than 20%, and as we keep scrolling, 224 224 00:12:14,070 --> 00:12:18,690 then, then as this line hits here the top of the viewport, 225 225 00:12:18,690 --> 00:12:20,740 we should get another one, which is when 226 226 00:12:20,740 --> 00:12:23,503 this zero here is again reached. 227 227 00:12:24,853 --> 00:12:25,686 So let's try that. 228 228 00:12:26,658 --> 00:12:27,808 And indeed, here it is. 229 229 00:12:29,392 --> 00:12:31,410 So we are back to intersection ratio at zero, 230 230 00:12:31,410 --> 00:12:35,113 and the element is no longer visible, all right? 231 231 00:12:36,320 --> 00:12:40,600 So this is how the intersection observer API works, 232 232 00:12:40,600 --> 00:12:43,620 and let's now quickly use this in order to implement 233 233 00:12:43,620 --> 00:12:46,290 our sticky navigation, because at this point, 234 234 00:12:46,290 --> 00:12:48,920 I'm sure that you can already imagine 235 235 00:12:48,920 --> 00:12:52,360 how this can be very useful for implementing this 236 236 00:12:52,360 --> 00:12:53,353 in an easy way. 237 237 00:12:57,044 --> 00:12:58,394 So, let's think about this. 238 238 00:12:59,472 --> 00:13:01,943 When do we want our navigation to become sticky? 239 239 00:13:03,449 --> 00:13:05,520 Well, we want that to happen essentially 240 240 00:13:05,520 --> 00:13:08,453 when the header moves completely out of view. 241 241 00:13:09,722 --> 00:13:11,522 So basically, all of this part here, 242 242 00:13:12,426 --> 00:13:15,347 which is the header, when we can no longer see it, 243 243 00:13:15,347 --> 00:13:19,283 that's when we want then to display the navigation, okay? 244 244 00:13:20,450 --> 00:13:21,283 And so this time, we are going 245 245 00:13:21,283 --> 00:13:23,263 to observe the header element. 246 246 00:13:25,691 --> 00:13:27,113 So let's start by selecting that. 247 247 00:13:33,397 --> 00:13:37,923 And it is an element with the class of header, all right? 248 248 00:13:39,155 --> 00:13:41,883 Let's actually get rid of this part here. 249 249 00:13:45,273 --> 00:13:47,953 Okay, and now let's create our observer. 250 250 00:13:51,375 --> 00:13:53,725 So this time I'm calling it the headerObserver, 251 251 00:13:54,943 --> 00:13:57,293 just so we know exactly what is being observed. 252 252 00:13:58,219 --> 00:14:00,253 So new IntersectionObserver, 253 253 00:14:02,769 --> 00:14:04,600 and then I'm gonna pass in the arguments later, 254 254 00:14:04,600 --> 00:14:07,330 and then I will use the headerObserver 255 255 00:14:09,114 --> 00:14:12,173 to observe the header. 256 256 00:14:13,120 --> 00:14:13,953 Okay? 257 257 00:14:15,137 --> 00:14:18,210 So this all kind of sound like normal English sentences 258 258 00:14:18,210 --> 00:14:20,713 if we read it like this, right? 259 259 00:14:22,730 --> 00:14:25,560 So here we again need a callback function, 260 260 00:14:25,560 --> 00:14:27,260 so let's just call this stickyNav, 261 261 00:14:28,658 --> 00:14:30,790 actually, and then again the options. 262 262 00:14:30,790 --> 00:14:32,630 Now this time, I will just create 263 263 00:14:32,630 --> 00:14:36,703 the options object right here, all right? 264 264 00:14:39,704 --> 00:14:41,873 And so the root will once again be null, 265 265 00:14:43,401 --> 00:14:46,964 because we are again interested in the entire viewport, 266 266 00:14:46,964 --> 00:14:48,093 and then the threshold. 267 267 00:14:50,094 --> 00:14:52,360 So, I said that we are interested in showing 268 268 00:14:52,360 --> 00:14:55,200 the sticky navigation as soon as this header 269 269 00:14:55,200 --> 00:14:57,203 scrolls completely out of view. 270 270 00:14:58,448 --> 00:15:00,098 So what threshold does that mean? 271 271 00:15:01,470 --> 00:15:03,373 Well, that's just zero, right? 272 272 00:15:04,496 --> 00:15:08,200 So when 0% of the header here is visible, 273 273 00:15:08,200 --> 00:15:10,383 then we want something to happen. 274 274 00:15:14,340 --> 00:15:17,883 Okay, and now let's define this function here, 275 275 00:15:18,787 --> 00:15:21,420 and here we will have exactly the functionality 276 276 00:15:21,420 --> 00:15:24,850 that we want to happen, so to add and to remove 277 277 00:15:24,850 --> 00:15:26,033 the sticky class. 278 278 00:15:27,663 --> 00:15:29,830 So this function gets the entries, and this time, 279 279 00:15:29,830 --> 00:15:31,830 I'm not gonna specify the observer, 280 280 00:15:31,830 --> 00:15:33,913 because in this case, we don't need it. 281 281 00:15:36,048 --> 00:15:37,948 Also, there's only one threshold here, 282 282 00:15:38,964 --> 00:15:41,377 so I don't need to loop over the entries. 283 283 00:15:41,377 --> 00:15:42,703 We can simply get the first one, 284 284 00:15:44,256 --> 00:15:46,778 and let's actually use destructuring 285 285 00:15:46,778 --> 00:15:49,733 to get the first element, so entry, 286 286 00:15:51,006 --> 00:15:53,006 to get the first element out of entries. 287 287 00:15:54,930 --> 00:15:56,623 And remember that this is the same 288 288 00:15:56,623 --> 00:15:59,803 as writing entries zero, right? 289 289 00:16:02,688 --> 00:16:05,973 So, let's just start by taking a look at this entry, 290 290 00:16:07,045 --> 00:16:08,193 just to see if it works. 291 291 00:16:10,208 --> 00:16:12,820 And here, one more time, we already get something, 292 292 00:16:12,820 --> 00:16:15,460 so I'm not sure why that is actually, 293 293 00:16:15,460 --> 00:16:18,163 because this has nothing to do with our threshold. 294 294 00:16:19,910 --> 00:16:23,283 All right, but let's just wait for the next one, 295 295 00:16:24,255 --> 00:16:26,251 and so it should be appearing soon, 296 296 00:16:26,251 --> 00:16:28,970 because our target, so this header is almost moving 297 297 00:16:28,970 --> 00:16:33,183 out of the view, and indeed, here it is. 298 298 00:16:35,268 --> 00:16:36,830 So intersection ratio is zero, 299 299 00:16:36,830 --> 00:16:38,893 and it is no longer intersecting. 300 300 00:16:41,135 --> 00:16:43,690 And so now, let's actually create the logic 301 301 00:16:43,690 --> 00:16:46,083 of adding and removing the classes. 302 302 00:16:49,055 --> 00:16:51,830 So basically what we want to do 303 303 00:16:51,830 --> 00:16:55,393 is to first add it here, and so let's start with that. 304 304 00:17:00,414 --> 00:17:03,414 But you see that now it actually already applied this class, 305 305 00:17:04,933 --> 00:17:06,470 and that's because right now, our target element 306 306 00:17:06,470 --> 00:17:10,400 is intersecting the root, so the viewport, all right? 307 307 00:17:10,400 --> 00:17:12,163 So we will use that in a second. 308 308 00:17:13,565 --> 00:17:15,233 Let's just see what happens next. 309 309 00:17:17,222 --> 00:17:20,713 So here we will now get our next one, right? 310 310 00:17:22,023 --> 00:17:24,170 And so now it is no longer intersecting. 311 311 00:17:24,170 --> 00:17:27,683 So intersection ratio zero, but no longer intersecting. 312 312 00:17:28,867 --> 00:17:29,750 And so this is actually the condition 313 313 00:17:29,750 --> 00:17:32,550 that we are interested in, right? 314 314 00:17:32,550 --> 00:17:36,220 So only when the header is not intersecting the viewport 315 315 00:17:36,220 --> 00:17:39,020 is when we want to add that sticky class, 316 316 00:17:39,020 --> 00:17:42,683 because watch what happens when we move back up. 317 317 00:17:46,289 --> 00:17:51,090 So right now, you see we got this new entry here, 318 318 00:17:53,370 --> 00:17:57,473 and so in this case, it is again intersecting, 319 319 00:17:58,584 --> 00:18:01,310 and so, and in this case where we are scrolling up 320 320 00:18:01,310 --> 00:18:05,570 is when we actually want to remove that sticky class, right? 321 321 00:18:05,570 --> 00:18:07,350 So we are entering the header again, 322 322 00:18:07,350 --> 00:18:09,190 and so that's the point in time 323 323 00:18:09,190 --> 00:18:12,603 where we want the sticky class to be gone. 324 324 00:18:14,064 --> 00:18:16,550 And so now we can use this intersecting property 325 325 00:18:16,550 --> 00:18:17,913 to do exactly that. 326 326 00:18:19,931 --> 00:18:24,931 So we can say that if the entry.isIntersecting is false, 327 327 00:18:30,115 --> 00:18:31,393 basically, then do this. 328 328 00:18:33,578 --> 00:18:34,411 Right? 329 329 00:18:34,411 --> 00:18:38,670 So again, when the target is not intersecting the root, 330 330 00:18:38,670 --> 00:18:41,553 then we want the sticky class to be applied. 331 331 00:18:42,860 --> 00:18:45,553 And else, we want to remove it. 332 332 00:18:53,031 --> 00:18:53,864 So let's reload, 333 333 00:18:56,346 --> 00:18:59,403 and now indeed, the sticky class is no longer there, okay? 334 334 00:19:02,033 --> 00:19:04,040 And now watch what happens as this line 335 335 00:19:04,040 --> 00:19:08,423 reaches the top there, then yeah, here it is. 336 336 00:19:09,684 --> 00:19:11,240 So there is our sticky navigation, 337 337 00:19:11,240 --> 00:19:14,308 so that's great, and indeed, it is because 338 338 00:19:14,308 --> 00:19:16,653 it is now no longer intersecting. 339 339 00:19:18,393 --> 00:19:20,800 And so now the final test is when we move back up, 340 340 00:19:20,800 --> 00:19:25,120 then it is gone, and so as we scroll around this point, 341 341 00:19:25,120 --> 00:19:27,810 it will basically add and remove the class 342 342 00:19:27,810 --> 00:19:29,883 according to the scrolling direction. 343 343 00:19:31,444 --> 00:19:33,910 Now we're actually not really done yet 344 344 00:19:33,910 --> 00:19:35,890 because I want to make this a little bit different, 345 345 00:19:35,890 --> 00:19:36,913 or a bit better. 346 346 00:19:38,105 --> 00:19:39,303 So let me show you the demo here, 347 347 00:19:40,784 --> 00:19:42,833 so just to make sure, I'm gonna reload it here, 348 348 00:19:45,000 --> 00:19:47,193 never mind this effect you just saw here. 349 349 00:19:48,345 --> 00:19:50,545 But watch when the navigation comes in here. 350 350 00:19:53,959 --> 00:19:55,710 So you see when that happens, it's basically 351 351 00:19:55,710 --> 00:19:58,370 when the distance between the start of the section 352 352 00:19:58,370 --> 00:20:01,210 and the viewport here is just the same 353 353 00:20:01,210 --> 00:20:02,900 as the navigation. 354 354 00:20:02,900 --> 00:20:04,100 You see that? 355 355 00:20:04,100 --> 00:20:07,283 And so like this, the navigation doesn't overlap 356 356 00:20:07,283 --> 00:20:09,483 this section here right in the beginning. 357 357 00:20:11,657 --> 00:20:14,180 So here the navigation comes exactly before 358 358 00:20:14,180 --> 00:20:16,043 the first section starts. 359 359 00:20:17,362 --> 00:20:18,890 And so let's implement it here as well 360 360 00:20:18,890 --> 00:20:22,120 and thankfully, that's pretty easy to do, 361 361 00:20:22,120 --> 00:20:26,440 and we can do it by specifying another property here 362 362 00:20:26,440 --> 00:20:30,850 which is the rootMargin, okay? 363 363 00:20:30,850 --> 00:20:34,490 And this root margin here, for example 90, 364 364 00:20:34,490 --> 00:20:37,890 is a box of 90 pixels that will be applied 365 365 00:20:37,890 --> 00:20:40,373 outside of our target element, 366 366 00:20:41,588 --> 00:20:43,600 so of our header here, okay? 367 367 00:20:43,600 --> 00:20:45,909 And so now it is as if the header 368 368 00:20:45,909 --> 00:20:50,563 did not stop right here, but instead, out here. 369 369 00:20:51,630 --> 00:20:53,202 All right? 370 370 00:20:53,202 --> 00:20:55,880 So as if the header went all the way here. 371 371 00:20:55,880 --> 00:21:00,800 Now we actually want the header to basically stop here. 372 372 00:21:00,800 --> 00:21:02,473 And so that's -90. 373 373 00:21:04,300 --> 00:21:08,200 Okay, and here we then need to specify also the unit, 374 374 00:21:08,200 --> 00:21:11,600 which has got to be pixels, so unfortunately, 375 375 00:21:11,600 --> 00:21:15,940 percentage does not work, and also rem does not work 376 376 00:21:15,940 --> 00:21:18,340 so it has to be pixels, and so that's why 377 377 00:21:18,340 --> 00:21:20,330 I'm using 90 pixels here. 378 378 00:21:20,330 --> 00:21:23,113 And 90 is the height of the navigation, 379 379 00:21:24,310 --> 00:21:26,493 and so let's test this here again. 380 380 00:21:28,034 --> 00:21:31,483 So let's see, and so let's wait for it, 381 381 00:21:32,370 --> 00:21:33,810 and did you see that? 382 382 00:21:33,810 --> 00:21:38,240 Indeed, now the navigation appeared exactly 90 pixels 383 383 00:21:38,240 --> 00:21:40,933 before the threshold was actually reached. 384 384 00:21:42,359 --> 00:21:45,453 So you see, now we get the event here even later, 385 385 00:21:46,310 --> 00:21:48,483 and all the data here is still the same. 386 386 00:21:49,540 --> 00:21:51,990 This is simply a visual margin that gets applied. 387 387 00:21:53,429 --> 00:21:54,810 So you can play around with this as well 388 388 00:21:54,810 --> 00:21:57,400 with the difference between a positive 389 389 00:21:57,400 --> 00:22:01,920 and a negative margin to figure out really how this works, 390 390 00:22:01,920 --> 00:22:04,660 because this root margin here is very important 391 391 00:22:04,660 --> 00:22:08,393 to specify correctly, as we need it in many situations. 392 392 00:22:09,845 --> 00:22:12,320 Now just as one final detail, let's actually calculate 393 393 00:22:12,320 --> 00:22:14,083 this height here dynamically. 394 394 00:22:15,020 --> 00:22:19,423 And for that, we can use the getBoundingClientRect function, 395 395 00:22:21,980 --> 00:22:25,293 because for example if you have a responsive site, 396 396 00:22:26,548 --> 00:22:29,322 then probably the size of all your elements 397 397 00:22:29,322 --> 00:22:33,152 will change at certain points, and then it's not a good idea 398 398 00:22:33,152 --> 00:22:37,000 to have this 90 pixels here hard coded 399 399 00:22:37,000 --> 00:22:38,200 right there in the code. 400 400 00:22:39,485 --> 00:22:40,500 Let's just take a look so we see 401 401 00:22:40,500 --> 00:22:42,333 what we actually need to get. 402 402 00:22:45,387 --> 00:22:48,576 So this is the rectangle, and so here we actually 403 403 00:22:48,576 --> 00:22:49,726 have a height property. 404 404 00:22:50,788 --> 00:22:52,503 So this is where that 90 comes from. 405 405 00:22:54,680 --> 00:22:57,193 So let's read that directly here, height. 406 406 00:22:58,720 --> 00:23:00,923 All right, and so now here we can use that. 407 407 00:23:04,260 --> 00:23:05,653 Let's create a nice template string here, 408 408 00:23:09,944 --> 00:23:14,611 navHeight, and with that, I believe we're actually done. 409 409 00:23:16,625 --> 00:23:17,870 All right, and of course this works 410 410 00:23:17,870 --> 00:23:21,803 no matter how large or how small the viewport is. 411 411 00:23:27,587 --> 00:23:29,680 Okay, now it works beautifully and correctly 412 412 00:23:29,680 --> 00:23:33,040 in all situations and this is a lot more performant 413 413 00:23:33,040 --> 00:23:35,770 and a lot better than the solution that I showed you 414 414 00:23:35,770 --> 00:23:37,023 in the previous lecture. 415 415 00:23:38,216 --> 00:23:39,780 So play around with this but we will actually 416 416 00:23:39,780 --> 00:23:42,680 also have I think two more examples 417 417 00:23:42,680 --> 00:23:46,260 with the intersection observer API coming up 418 418 00:23:46,260 --> 00:23:48,620 and so that's gonna be another great opportunity 419 419 00:23:48,620 --> 00:23:51,580 to learn how this API really works, 420 420 00:23:51,580 --> 00:23:54,300 because it's quite important actually to do things 421 421 00:23:54,300 --> 00:23:57,204 on certain positions on the page, 422 422 00:23:57,204 --> 00:23:58,754 so things related to scrolling. 37589