1 00:00:01,160 --> 00:00:02,580 So in this section, 2 00:00:02,580 --> 00:00:04,870 we're going to make JavaScript interact 3 00:00:04,870 --> 00:00:08,320 with a webpage for the very first time. 4 00:00:08,320 --> 00:00:12,710 And the technical term for that is doing DOM Manipulation. 5 00:00:12,710 --> 00:00:14,090 Now, in the last lecture, 6 00:00:14,090 --> 00:00:17,580 you already selected an element from a page. 7 00:00:17,580 --> 00:00:19,970 And what that means is that you, kind of, 8 00:00:19,970 --> 00:00:23,180 interacted with the DOM already. 9 00:00:23,180 --> 00:00:24,450 So in this lecture, 10 00:00:24,450 --> 00:00:28,203 let's learn what the DOM actually is and how it works. 11 00:00:30,040 --> 00:00:33,010 So what is the DOM actually? 12 00:00:33,010 --> 00:00:37,310 Well, DOM stands for Document Object Model, and it is, 13 00:00:37,310 --> 00:00:42,310 basically, a structured representation of HTML documents. 14 00:00:42,490 --> 00:00:46,480 The DOM allows us to use JavaScript to access HTML elements 15 00:00:46,480 --> 00:00:50,000 and styles in order to manipulate them. 16 00:00:50,000 --> 00:00:53,280 For example, we will be able to change text, 17 00:00:53,280 --> 00:00:56,650 to change HTML attributes and also to change 18 00:00:56,650 --> 00:00:59,870 CSS styles from our JavaScript. 19 00:00:59,870 --> 00:01:04,000 So we can say that DOM is basically a connection point 20 00:01:04,000 --> 00:01:07,453 between HTML documents and JavaScript code. 21 00:01:08,290 --> 00:01:10,800 Now, the DOM is automatically created 22 00:01:10,800 --> 00:01:14,680 by the browser as soon as the HTML page loads. 23 00:01:14,680 --> 00:01:18,840 And it's stored in a tree structure like this one. 24 00:01:18,840 --> 00:01:23,090 In this tree, each HTML element is one object. 25 00:01:23,090 --> 00:01:26,360 And so let's now take a look at this DOM structure 26 00:01:26,360 --> 00:01:28,273 in a little bit more detail. 27 00:01:29,700 --> 00:01:34,630 And to illustrate this here is a very simple HTML document, 28 00:01:34,630 --> 00:01:36,890 and here is what a DOM tree 29 00:01:36,890 --> 00:01:40,053 corresponding to this HTML looks like. 30 00:01:41,090 --> 00:01:45,290 So, as I already mentioned, this is a tree structure, 31 00:01:45,290 --> 00:01:49,110 which looks a bit like a family tree, right? 32 00:01:49,110 --> 00:01:52,070 And actually we used the terms, child element, 33 00:01:52,070 --> 00:01:55,740 parent element, sibling element and so on, 34 00:01:55,740 --> 00:01:59,013 when we talk about the DOM tree and DOM manipulation. 35 00:01:59,850 --> 00:02:04,070 Anyway, as you can see for each element in the HTML, 36 00:02:04,070 --> 00:02:07,120 there is one element node and the DOM tree, 37 00:02:07,120 --> 00:02:08,910 and we can access and interact 38 00:02:08,910 --> 00:02:12,440 with each of these nodes using JavaScript. 39 00:02:12,440 --> 00:02:16,920 Okay, so the DOM always starts with the document object, 40 00:02:16,920 --> 00:02:18,740 right at the very top. 41 00:02:18,740 --> 00:02:21,230 And document is a special object 42 00:02:21,230 --> 00:02:23,420 that we have access to in JavaScript. 43 00:02:23,420 --> 00:02:27,860 And this object serves as an entry point into the DOM. 44 00:02:27,860 --> 00:02:30,880 Remember how you used document dot query selector 45 00:02:30,880 --> 00:02:34,140 in the last lecture to select an element. 46 00:02:34,140 --> 00:02:37,380 So that means that the query selector method 47 00:02:37,380 --> 00:02:40,400 is available on the document object. 48 00:02:40,400 --> 00:02:42,890 And so that's why we say that document 49 00:02:42,890 --> 00:02:45,140 is the entry point to the DOM, 50 00:02:45,140 --> 00:02:48,143 because we need it to start selecting elements. 51 00:02:49,110 --> 00:02:53,260 All right, then the first child element of document 52 00:02:53,260 --> 00:02:57,220 is usually the HTML element, because that's usually 53 00:02:57,220 --> 00:03:00,550 the root element in all HTML documents. 54 00:03:00,550 --> 00:03:05,550 Next, HTML usually has two child elements, head and body. 55 00:03:05,950 --> 00:03:07,950 And so of course you can also 56 00:03:07,950 --> 00:03:10,836 find them here in the DOM tree. 57 00:03:10,836 --> 00:03:13,640 In the HTML, they are adjacent elements, 58 00:03:13,640 --> 00:03:17,310 and so they are siblings in our DOM as well. 59 00:03:17,310 --> 00:03:19,330 Then, as we keep going deeper 60 00:03:19,330 --> 00:03:21,920 into the nested HTML structure, 61 00:03:21,920 --> 00:03:26,000 we keep adding more and more children to the DOM tree. 62 00:03:26,000 --> 00:03:30,150 So inside head and body, you have more child elements, 63 00:03:30,150 --> 00:03:32,410 and the two sections and the body, 64 00:03:32,410 --> 00:03:35,370 even have child elements themselves. 65 00:03:35,370 --> 00:03:37,830 And from there, it goes even deeper 66 00:03:37,830 --> 00:03:41,440 because the first paragraph also has a child, 67 00:03:41,440 --> 00:03:43,193 which is this link element here. 68 00:03:44,160 --> 00:03:45,740 And with that, finally, 69 00:03:45,740 --> 00:03:49,660 we have all our HTML elements in the DOM tree. 70 00:03:49,660 --> 00:03:54,150 But a Dom tree actually has more than just element nodes. 71 00:03:54,150 --> 00:03:57,250 It also has nodes for all the text itself, 72 00:03:57,250 --> 00:03:59,930 comments and other stuff, 73 00:03:59,930 --> 00:04:02,470 because basically the rule is that 74 00:04:02,470 --> 00:04:07,470 whatever is in the HTML document also has to be in the DOM. 75 00:04:07,540 --> 00:04:10,300 And so, as you see, the DOM really is 76 00:04:10,300 --> 00:04:13,970 a complete representation of the HTML document, 77 00:04:13,970 --> 00:04:17,480 so that we can manipulate it in complex ways. 78 00:04:17,480 --> 00:04:20,310 And with this, you should now have a good overview 79 00:04:20,310 --> 00:04:23,423 of how the DOM works and what it looks like. 80 00:04:24,750 --> 00:04:27,920 But before we finish, I need to clarify something 81 00:04:27,920 --> 00:04:31,360 that many beginners find confusing. 82 00:04:31,360 --> 00:04:34,560 So, many people believe that the DOM 83 00:04:34,560 --> 00:04:36,870 and all the methods and properties 84 00:04:36,870 --> 00:04:39,660 that we can use to manipulate the DOM, 85 00:04:39,660 --> 00:04:42,420 such as documented or the query selector 86 00:04:42,420 --> 00:04:47,310 and lots of other stuff are actually part of JavaScript. 87 00:04:47,310 --> 00:04:50,420 However, this is not the case. 88 00:04:50,420 --> 00:04:54,490 Remember that JavaScript is actually just a dialect 89 00:04:54,490 --> 00:04:57,100 of the ECMAScript specification, 90 00:04:57,100 --> 00:05:01,940 and all this DOM related stuff is simply not in there. 91 00:05:01,940 --> 00:05:03,450 So up until this point, 92 00:05:03,450 --> 00:05:06,630 we have only used the JavaScript language itself. 93 00:05:06,630 --> 00:05:08,730 But starting in this section, 94 00:05:08,730 --> 00:05:12,060 we will also use JavaScript in a browser. 95 00:05:12,060 --> 00:05:14,720 I mean, sure, we have used Google Chrome 96 00:05:14,720 --> 00:05:17,750 to run our code in the developer console, 97 00:05:17,750 --> 00:05:19,890 but that's not what I mean here. 98 00:05:19,890 --> 00:05:22,320 What I mean is to manipulate webpages 99 00:05:22,320 --> 00:05:26,170 that are actually displayed and rendered in the browser, 100 00:05:26,170 --> 00:05:28,793 just like any normal website that you know. 101 00:05:29,650 --> 00:05:30,483 Okay. 102 00:05:30,483 --> 00:05:32,167 But, now you might ask, 103 00:05:32,167 --> 00:05:35,940 "If the DOM is not a part of the JavaScript language, 104 00:05:35,940 --> 00:05:38,370 then how does this all work?" 105 00:05:38,370 --> 00:05:41,130 Well, the DOM and DOM methods 106 00:05:41,130 --> 00:05:45,440 are actually part of something called the web APIs. 107 00:05:45,440 --> 00:05:48,120 So the web API APIs are like libraries 108 00:05:48,120 --> 00:05:49,970 that browsers implement 109 00:05:49,970 --> 00:05:53,490 and that we can access from our JavaScript code. 110 00:05:53,490 --> 00:05:57,410 And API stands for Application Programming Interface. 111 00:05:57,410 --> 00:05:59,460 But more about that later. 112 00:05:59,460 --> 00:06:01,540 For now, what you need to know 113 00:06:01,540 --> 00:06:03,530 is that a web APIs are, basically, 114 00:06:03,530 --> 00:06:07,120 libraries that are also written in JavaScript 115 00:06:07,120 --> 00:06:10,930 and that are automatically available for us to use. 116 00:06:10,930 --> 00:06:13,320 So all this happens behind the scenes, 117 00:06:13,320 --> 00:06:17,810 we don't have to import or do anything, okay? 118 00:06:17,810 --> 00:06:20,820 And there is actually an official DOM specification 119 00:06:20,820 --> 00:06:22,530 that browsers implement, 120 00:06:22,530 --> 00:06:24,920 which is the reason why DOM manipulation 121 00:06:24,920 --> 00:06:26,853 works the same in all browsers. 122 00:06:27,750 --> 00:06:29,370 Now, besides the DOM, 123 00:06:29,370 --> 00:06:32,290 there are actually a ton more web APIs, 124 00:06:32,290 --> 00:06:36,770 such as timers, the fetch API, and many more. 125 00:06:36,770 --> 00:06:40,370 Again, we will learn a lot more about this later on. 126 00:06:40,370 --> 00:06:43,290 For now, let's finally start our project 127 00:06:43,290 --> 00:06:46,073 and do some DOM manipulation in practice.