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These are the user uploaded subtitles that are being translated: 1 1 00:00:01,180 --> 00:00:04,460 Dealing and working with data is the main thing 2 2 00:00:04,460 --> 00:00:06,820 that we do as developers. 3 3 00:00:06,820 --> 00:00:08,150 And that's the reason why, 4 4 00:00:08,150 --> 00:00:10,010 since the beginning of the course, 5 5 00:00:10,010 --> 00:00:11,070 we have been working 6 6 00:00:11,070 --> 00:00:13,980 with JavaScripts built-in data structures, 7 7 00:00:13,980 --> 00:00:16,800 like arrays and objects. 8 8 00:00:16,800 --> 00:00:18,740 Then in the last few lectures 9 9 00:00:18,740 --> 00:00:21,550 we learned about two new data structures 10 10 00:00:21,550 --> 00:00:24,470 which are sets and objects. 11 11 00:00:24,470 --> 00:00:26,840 So now we have four data structures 12 12 00:00:26,840 --> 00:00:28,690 from which we can choose. 13 13 00:00:28,690 --> 00:00:31,710 And so I decided to create this quick lecture 14 14 00:00:31,710 --> 00:00:35,750 which will show you the pros and cons of each data structure 15 15 00:00:35,750 --> 00:00:38,363 and also when to choose each of them. 16 16 00:00:40,380 --> 00:00:43,470 And I want to start this video by quickly categorizing 17 17 00:00:43,470 --> 00:00:46,800 where data can actually come from. 18 18 00:00:46,800 --> 00:00:50,690 So there are essentially three sources of data. 19 19 00:00:50,690 --> 00:00:52,610 First, the data can be written 20 20 00:00:52,610 --> 00:00:56,970 within the program source code itself like status messages 21 21 00:00:56,970 --> 00:01:01,840 that will be displayed on a webpage based on user actions. 22 22 00:01:01,840 --> 00:01:05,300 Second, data can come from the user interface. 23 23 00:01:05,300 --> 00:01:07,090 So from the webpage, 24 24 00:01:07,090 --> 00:01:11,430 it can either be data that the user inputs into some form 25 25 00:01:11,430 --> 00:01:15,330 or data test already written somehow in the DOM. 26 26 00:01:15,330 --> 00:01:19,430 For example, this can be the users tasks in a todo app 27 27 00:01:19,430 --> 00:01:24,140 or expenses in a budget app or anything like that. 28 28 00:01:24,140 --> 00:01:27,870 Finally, data can come from external sources 29 29 00:01:27,870 --> 00:01:30,970 which is usually a web API. 30 30 00:01:30,970 --> 00:01:33,700 Now what is a web API? 31 31 00:01:33,700 --> 00:01:38,110 Well, API stands for Application Programming Interface 32 32 00:01:38,110 --> 00:01:41,420 and we can basically use a web API to get data 33 33 00:01:41,420 --> 00:01:44,020 from other web applications. 34 34 00:01:44,020 --> 00:01:46,620 For example we can use a web API 35 35 00:01:46,620 --> 00:01:50,890 to get the current weather in any city or data about movies 36 36 00:01:50,890 --> 00:01:53,140 or currency conversion rates 37 37 00:01:53,140 --> 00:01:56,760 and really every kind of data that you can imagine. 38 38 00:01:56,760 --> 00:02:00,073 And we will learn how all that works later in the course. 39 39 00:02:00,970 --> 00:02:03,810 So no matter where the data comes from 40 40 00:02:03,810 --> 00:02:06,010 and what kind of data it is, 41 41 00:02:06,010 --> 00:02:09,140 we usually always have collections of data 42 42 00:02:09,140 --> 00:02:12,040 that we then need to store somewhere. 43 43 00:02:12,040 --> 00:02:15,330 And so where do we store collections of data? 44 44 00:02:15,330 --> 00:02:19,550 That's right, we use data structures, but as you know 45 45 00:02:19,550 --> 00:02:23,440 there are four built-in data structures in JavaScript. 46 46 00:02:23,440 --> 00:02:27,200 And so now we need a way of deciding between them, 47 47 00:02:27,200 --> 00:02:29,260 but it's not that hard. 48 48 00:02:29,260 --> 00:02:31,760 So the first decision is this 49 49 00:02:31,760 --> 00:02:34,810 do we just need a simple list of values? 50 50 00:02:34,810 --> 00:02:39,210 If so, then we're gonna use an array or a set. 51 51 00:02:39,210 --> 00:02:42,650 But on the other hand if we need key value pairs, 52 52 00:02:42,650 --> 00:02:45,083 then we need an object or a map. 53 53 00:02:45,940 --> 00:02:49,730 So the big difference here is that with a key value pair 54 54 00:02:49,730 --> 00:02:53,853 we have a way of describing the values, so by using the key. 55 55 00:02:54,750 --> 00:02:58,860 On the other hand, in a list like an array or a set, 56 56 00:02:58,860 --> 00:03:03,860 we simply have the values without any description, okay? 57 57 00:03:04,050 --> 00:03:05,780 Now, as a quick example, 58 58 00:03:05,780 --> 00:03:09,400 let's go back to getting data from a web API 59 59 00:03:09,400 --> 00:03:12,170 because in modern JavaScript applications 60 60 00:03:12,170 --> 00:03:15,730 that's usually the most common source of data. 61 61 00:03:15,730 --> 00:03:20,670 So data from web APIs usually comes in a special data format 62 62 00:03:20,670 --> 00:03:25,070 called JSON which looks like this example here. 63 63 00:03:25,070 --> 00:03:29,640 So JSON is essentially just text so a long string, 64 64 00:03:29,640 --> 00:03:33,030 but it can easily be converted to JavaScript objects 65 65 00:03:33,030 --> 00:03:35,500 because it uses the same formatting 66 66 00:03:35,500 --> 00:03:38,343 as JavaScript objects and arrays. 67 67 00:03:39,190 --> 00:03:43,200 So here we have three objects that describe recipes. 68 68 00:03:43,200 --> 00:03:47,380 We have the values in green, like the title and a publisher. 69 69 00:03:47,380 --> 00:03:48,940 And it makes complete sense 70 70 00:03:48,940 --> 00:03:53,220 that these values are then described using a key. 71 71 00:03:53,220 --> 00:03:55,430 Otherwise we would have no idea 72 72 00:03:55,430 --> 00:03:59,220 what the different values actually are, right? 73 73 00:03:59,220 --> 00:04:02,080 So key value pairs are essential here 74 74 00:04:02,080 --> 00:04:05,480 and that's why this data is stored in an object, 75 75 00:04:05,480 --> 00:04:07,380 not an array. 76 76 00:04:07,380 --> 00:04:10,550 Now, each of these recipe objects in itself 77 77 00:04:10,550 --> 00:04:12,760 can be seen as a value. 78 78 00:04:12,760 --> 00:04:14,660 And since we have many of them, 79 79 00:04:14,660 --> 00:04:17,960 it means that we have again a collection of data 80 80 00:04:17,960 --> 00:04:22,130 and therefore we need a data structure to store them. 81 81 00:04:22,130 --> 00:04:26,210 Now, do we want to describe each of the objects? 82 82 00:04:26,210 --> 00:04:29,660 Well, it's not really necessary, is it? 83 83 00:04:29,660 --> 00:04:32,600 We already know they are all recipes 84 84 00:04:32,600 --> 00:04:35,900 and whatever information we need about the recipes 85 85 00:04:35,900 --> 00:04:39,750 is already stored right in each of the objects. 86 86 00:04:39,750 --> 00:04:42,900 So all we want is basically a simple list 87 87 00:04:42,900 --> 00:04:45,820 where all the recipes are held together. 88 88 00:04:45,820 --> 00:04:50,820 And so here an array is the perfect data structure for debt. 89 89 00:04:50,870 --> 00:04:54,190 And in fact, creating an array of objects 90 90 00:04:54,190 --> 00:04:57,260 is extremely common in JavaScript. 91 91 00:04:57,260 --> 00:05:01,020 Now you will be working with this kind of data all the time 92 92 00:05:01,020 --> 00:05:03,670 as a professional JavaScript developer. 93 93 00:05:03,670 --> 00:05:06,973 And that's why I'm placing so much focus on this here. 94 94 00:05:07,840 --> 00:05:12,440 Okay, now before we move on to compare array, sets, 95 95 00:05:12,440 --> 00:05:15,780 objects and maps, I quickly want to mention 96 96 00:05:15,780 --> 00:05:18,634 that there are also Weaksets 97 97 00:05:18,634 --> 00:05:22,270 and WeakMaps data structures in JavaScript. 98 98 00:05:22,270 --> 00:05:25,100 Also, there are even more data structures 99 99 00:05:25,100 --> 00:05:26,970 that are used in programming, 100 100 00:05:26,970 --> 00:05:30,060 but which are not built into JavaScript. 101 101 00:05:30,060 --> 00:05:31,700 And just to mention a few, 102 102 00:05:31,700 --> 00:05:35,630 these can be stacks, queues, linked lists, trees, 103 103 00:05:35,630 --> 00:05:37,470 or hash tables. 104 104 00:05:37,470 --> 00:05:39,650 And these don't really matter for now 105 105 00:05:39,650 --> 00:05:42,090 but I still just wanted to let you know 106 106 00:05:42,090 --> 00:05:43,750 that there are more than just 107 107 00:05:43,750 --> 00:05:46,103 the four built-in data structures. 108 108 00:05:47,810 --> 00:05:49,640 But now let's talk a bit more 109 109 00:05:49,640 --> 00:05:52,750 about the built-in data structures. 110 110 00:05:52,750 --> 00:05:56,750 So you already know at this point how to use all of them, 111 111 00:05:56,750 --> 00:06:00,360 but it's important to know when to use them. 112 112 00:06:00,360 --> 00:06:05,020 So starting with arrays versus sets, we already know 113 113 00:06:05,020 --> 00:06:08,720 that we should use them for simple lists of values 114 114 00:06:08,720 --> 00:06:11,523 when we do not need to describe the values. 115 115 00:06:12,600 --> 00:06:16,230 Now you should use arrays whenever you need to store values 116 116 00:06:16,230 --> 00:06:21,020 in order and when these values might contain duplicates. 117 117 00:06:21,020 --> 00:06:23,200 Also you should always use arrays 118 118 00:06:23,200 --> 00:06:25,300 when you need to manipulate data 119 119 00:06:25,300 --> 00:06:29,240 because there are a ton of useful array methods. 120 120 00:06:29,240 --> 00:06:32,090 Now sets on the other hand should only be used 121 121 00:06:32,090 --> 00:06:35,230 when you are working with unique values, 122 122 00:06:35,230 --> 00:06:38,780 besides that you can also use sets in situations 123 123 00:06:38,780 --> 00:06:42,000 when high performance is really important 124 124 00:06:42,000 --> 00:06:45,060 because operations like searching for an item 125 125 00:06:45,060 --> 00:06:47,670 or deleting an item from a set can be 126 126 00:06:47,670 --> 00:06:52,260 up to 10 times faster in sets than in arrays. 127 127 00:06:52,260 --> 00:06:55,160 Now one great use case for sets 128 128 00:06:55,160 --> 00:06:57,963 is to remove duplicate values from an array 129 129 00:06:57,963 --> 00:07:01,180 like we already did before. 130 130 00:07:01,180 --> 00:07:04,640 So sets are really not meant to replace arrays 131 131 00:07:04,640 --> 00:07:06,300 but rather to compliment them 132 132 00:07:06,300 --> 00:07:10,280 whenever we are dealing with unique values. 133 133 00:07:10,280 --> 00:07:15,000 Okay, so now let's talk about objects versus maps 134 134 00:07:15,000 --> 00:07:16,550 and we already know that we should 135 135 00:07:16,550 --> 00:07:19,910 use these key value data structures 136 136 00:07:19,910 --> 00:07:24,890 whenever we need to describe the values using keys, right? 137 137 00:07:24,890 --> 00:07:29,050 But when to use objects and when to use maps. 138 138 00:07:29,050 --> 00:07:31,200 Well objects have been 139 139 00:07:31,200 --> 00:07:34,090 the traditional key value data structure 140 140 00:07:34,090 --> 00:07:38,700 simply because we didn't have maps before ES6, 141 141 00:07:38,700 --> 00:07:41,960 but using objects simply as key value stores 142 142 00:07:41,960 --> 00:07:44,750 has a couple of technical disadvantages. 143 143 00:07:44,750 --> 00:07:46,410 And that's why some people say 144 144 00:07:46,410 --> 00:07:49,910 that we've been abusing objects for this. 145 145 00:07:49,910 --> 00:07:52,860 Now maps on the other hand are way better suited 146 146 00:07:52,860 --> 00:07:55,140 for simple key value stores 147 147 00:07:55,140 --> 00:07:58,620 because they offer better performance in fact. 148 148 00:07:58,620 --> 00:08:02,240 Also map keys can have any data type 149 149 00:08:02,240 --> 00:08:04,590 and they're also easy to iterate 150 150 00:08:04,590 --> 00:08:08,350 and it's easy to compute the size of a map. 151 151 00:08:08,350 --> 00:08:11,160 However, the biggest advantage of objects 152 152 00:08:11,160 --> 00:08:15,590 is probably how easy it is to write them and to access data 153 153 00:08:15,590 --> 00:08:19,770 by simply using the dot or the brackets operator. 154 154 00:08:19,770 --> 00:08:24,460 Also most developers are already super used to objects. 155 155 00:08:24,460 --> 00:08:26,810 And so they simply keep using them 156 156 00:08:26,810 --> 00:08:28,923 for simple key value stores. 157 157 00:08:30,000 --> 00:08:33,170 Anyway, as a conclusion you should use maps 158 158 00:08:33,170 --> 00:08:36,600 when you simply need to map keys to values 159 159 00:08:36,600 --> 00:08:39,940 and also when you need keys that are not strings 160 160 00:08:39,940 --> 00:08:42,330 because as we saw in the last video, 161 161 00:08:42,330 --> 00:08:44,663 that can be very powerful sometimes. 162 162 00:08:45,590 --> 00:08:48,130 Now, if you need functions as values 163 163 00:08:48,130 --> 00:08:51,670 then you should absolutely use an object for that. 164 164 00:08:51,670 --> 00:08:55,540 So in objects, these functions are then called methods 165 165 00:08:55,540 --> 00:08:58,420 and you can use the this keyword to access properties 166 166 00:08:58,420 --> 00:09:02,790 of the same object, which is impossible in maps. 167 167 00:09:02,790 --> 00:09:05,350 Also, when working with JSON data, 168 168 00:09:05,350 --> 00:09:07,990 as we saw in the previous light 169 169 00:09:07,990 --> 00:09:11,310 you will probably be using objects for that as well 170 170 00:09:11,310 --> 00:09:14,680 unless you then want to convert the objects to maps, 171 171 00:09:14,680 --> 00:09:17,163 but that's usually not something that we do. 172 172 00:09:18,020 --> 00:09:21,630 So in fact, we still use objects all the time 173 173 00:09:21,630 --> 00:09:25,550 but maps are also a very important data structure right now 174 174 00:09:25,550 --> 00:09:27,873 and way more important than sets. 175 175 00:09:28,930 --> 00:09:32,990 Great, and with that, we wrap up this overview. 176 176 00:09:32,990 --> 00:09:37,023 I hope you found this useful and so let's now move on. 15751