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JavaScript and AJAX

Updating the DOM with getElementById


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JavaScript and AJAX

with Ray Villalobos

Video: Updating the DOM with getElementById

AJAX uses JavaScript to make changes to the current document through something called the DOM. This is the Document Object Model, and its job is to keep track of the structure of our HTML document. When you work with AJAX it's usually because you want to change something in your page after it has loaded. The easiest way to make a change in the DOM is through a JavaScript method called getElementByID. So the text editor that I use has a really nice DOM preview feature, so I'll turn that on right here, and you can see the DOM for our current HTML document. You can see that there is an HTML tag and inside the HTML tag we have a head section that has a couple of other elements, as well as a body section with just a script tag.

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JavaScript and AJAX
1h 12m Intermediate Jan 18, 2013

Viewers: in countries Watching now:

The ability to read data and communicate information asynchronously is fundamental to modern web applications. In this course, author Ray Villalobos takes a look at integrating AJAX (Asynchronous JavaScript and XML) with JavaScript and jQuery—a combination that makes it easy to work with dynamic data and reduces the number of requests to the server. The course first explains what AJAX is, and shows how to load and reload pages with pure JavaScript, update the DOM, and read and parse data in the XML and JSON formats. Next, learn how to read and write information between the server and the client with AJAX methods in jQuery, and build a dynamic search application that updates search results as you type.

Topics include:
  • What is AJAX?
  • Making requests asynchronous
  • Updating the DOM with getElementById
  • Reading JSON files
  • Working with jQuery and AJAX
  • Sending and searching JSON data
  • Incorporating CSS transitions
Subjects:
Developer Web Programming Languages Web Development
Software:
Ajax JavaScript
Author:
Ray Villalobos

Updating the DOM with getElementById

AJAX uses JavaScript to make changes to the current document through something called the DOM. This is the Document Object Model, and its job is to keep track of the structure of our HTML document. When you work with AJAX it's usually because you want to change something in your page after it has loaded. The easiest way to make a change in the DOM is through a JavaScript method called getElementByID. So the text editor that I use has a really nice DOM preview feature, so I'll turn that on right here, and you can see the DOM for our current HTML document. You can see that there is an HTML tag and inside the HTML tag we have a head section that has a couple of other elements, as well as a body section with just a script tag.

If we add another element here--let me add a headline--you will see that that element gets added into the document structure. If I add a paragraph, that also gets added, and if I create an element like an emphasis tag inside my paragraph, that gets added as a children of this paragraph object. Now, if you do add a div with an ID then that ID becomes a way that you can target that particular element.

So let me go ahead and save this and I'll switch over to my script.js file and I'll get rid of this console.log method that outputs our content to the console. Now, since we have an ID, we can easily target it in our JavaScript file. First we're going to need to create a variable and then find that element using getElementById. So I am going to replace this document.writeln command and I'll create a variable called modify. I'm going set that variable called modify to be equal to an element in the DOM with an ID of update.

Now that I have targeted that div in that variable, I can use that variable and modify the innerHTML, which is the HTML inside the element, to be whatever I want. In my case, I want to use the request and then look for the responseText. Let's go ahead and save this, and I'll switch over to my browser, and I'll load up the page and you could see the document has loaded Hello World into just the ID for update. So let me go ahead and right-click and Inspect Element.

We could see the div with the ID of update is right here, and I have inserted the text Hello World from my external document into that div. So getElementById combined with innerHTML gives you a very quick way to update any element in your DOM as long as it has an ID. This is sort of like a laser that lets you target an individual element very quickly.

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