This exercise is excerpted from Noble Desktop’s past JavaScript training materials. Noble Desktop now teaches JavaScript and the MERN Stack in our Full Stack Development Certificate. To learn current skills in web development, check out our coding bootcamps in NYC and live online.
Note: These materials are provided to give prospective students a sense of how we structure our class exercises and supplementary materials. During the course, you will get access to the accompanying class files, live instructor demonstrations, and hands-on instruction.
Topics covered in this JavaScript & jQuery tutorial:
Using Chrome’s DevTools, Selecting HTML elements with getElementById(), Manipulating selected elements, Getting & setting properties
Exercise Preview
Exercise Overview
In this exercise, we’ll take a look at what JavaScript is doing in the background. We’ll use Chrome’s DevTools to reveal the structure of the HTML document. We’ll select individual HTML elements and change them using JavaScript.
Getting Started
- On your Desktop, navigate into Class Files > yourname-JavaScript jQuery Class > Form-Fields folder.
- We want to use Chrome’s Developer Tools (DevTools), so we’ll open our page in Chrome. Ctrl–click (Mac) or Right–click (Windows) on form.html and choose Open With > Google Chrome.
- Ctrl–click (Mac) or Right–click (Windows) anywhere on the page and choose Inspect from the menu.
- We can now see Chrome’s DevTools. All modern browsers have Developer Tools. We can diagnose problems here and see what the browser is doing. We can also see all of the HTML, CSS, and JavaScript that the browser is reading.
The DevTools window has several groups of tools organized into tabbed panels. By default, you should see that the Elements panel is open.
In the Elements tab you can inspect an HTML element and see its precise markup. Mouse over any of the lines of HTML. As you do so, you should see the corresponding element highlighted in the browser window.
- At the top left of the DevTools window, click the
button. Now when you mouse over an element in the page, the corresponding HTML highlights in DevTools. - Click the button again to turn this off.
At the top of the DevTools window, click on the Console tab.
If there are JavaScript errors in the page, we will see them here. The Console is also a place where we can experiment safely with JavaScript.
- In the Console, type
alert('Hello');and hit Return (Mac) or Enter (Windows). - You should see a dialog that says Hello. Click OK to close the alert.
The Console lets us make temporary changes to the HTML page we’re looking at (even a working site). We’re going to experiment with hiding and showing various parts of this page.
Type document into the Console and hit Return (Mac) or Enter (Windows).
- You should see #document return in the Console. Mouse over the word #document and notice that the whole page is highlighted.
- Click the arrow next to #document to expand it. This is the whole HTML document, and contains everything on the page.
- Click the arrow next to
<body>to expand it, and see all of the contents of the body. Mouse over the various sections inside the
<body>and notice that those blocks of content highlight in the browser.
Selecting & Working with HTML Elements
We don’t typically want to make changes to the whole document all at once. We want to specify which HTML element we’d like to change. To get more specific, we can use the JavaScript method document.getElementById(). This dot syntax will become more familiar as we continue to dig deeper into accessing elements and their different properties as we go through the exercises.
- At the top left of the DevTools window, click the button.
- In the page, click on the text field under Name.
- In the DevTools, notice that the input with the ID nameField is highlighted.
In the DevTools, click on the Console tab.
In the Console, type
document.getElementById('nameField');About getElementById()
The getElementById() method allows you to target any HTML element in the document by placing its ID as a string inside the method’s parentheses. Please note that the capitalization of Id in the name of this method must be correct for the code to function. However tempting it may be to write getElementByID(), the function will not work written this way.
- Hit Return (Mac) or Enter (Windows).
You should see
<input id="nameField ... value="First and Last Name">in the Console.Mouse over this and notice that only the nameField input highlights. So far we’ve selected the whole element whose ID is nameField. We can get more specific and talk to this element’s styles by using dot syntax again.
- To save yourself some typing, press the Up Arrow key in the Console. This will show your last command so you don’t have to type it again. Very handy!
Add the following bold code to this previous command:
document.getElementById('nameField').style.display = 'none';This statement says to get the element with the ID nameField and set its display property to none, which will hide the input. Note that the property
value (‘none’) must be a string.- Hit Return (Mac) or Enter (Windows) to execute the code and notice that the input disappears!
- Let’s get the nameField to reappear. In the Console, press the Up Arrow key again to show your last command.
Change the code as shown in bold:
document.getElementById('nameField').style.display = 'block';Hit Return (Mac) or Enter (Windows). The input should reappear.
Getting & Setting Input Values
Inputs are special elements that we can use to collect information from our users. HTML input elements have a value attribute that changes when data is entered into the input. Let’s get and set the value of one of the inputs on this page.
Type the following into the Console:
document.getElementById('nameField').value;- Notice that the Console returns the text “First and Last Name”. This is the current value of the input tag.
- Let’s change the value to something else. On the page, click into the Name field and replace the text with your own name.
- Let’s see how JavaScript can get the new value of the input. Click on the Console to put your cursor there.
- Press the Up Arrow key to show your last command.
- Hit Return (Mac) or Enter (Windows) to execute the code.
- Notice that the Console should return the new value—your name!
- We can also use JavaScript to set the value of an input. Press the Up Arrow key again to show your last command.
Make the following changes shown in bold:
document.getElementById('nameField').value = 'example: John Doe';- Hit Return (Mac) or Enter (Windows) to execute the code.
- Notice in the page that the text field below Name should now say example: John Doe.
Code written in the Console will be lost when we refresh the page. Click the browser’s Reload button to see that your changes are gone.
While changes made in the Console are not permanent, it’s a great way to test small pieces of code.