Send your first script to the browser

Let’s add a hamburger menu to open and close your links on mobile screen sizes, requiring some client-side interactivity!

準備好……

• Create a hamburger menu component
• Write a <script> to allow your site visitors to open and close the navigation menu
• Move your JavaScript to its .js file

Build a Hamburger component

Section titled Build a Hamburger component

Create a <Hamburger /> component to open and close your mobile menu.

1. Create a file named Hamburger.astro in src/components/

2. Copy the following code into your component. This will represent your 3-line “hamburger” menu to open and close your navigation links on mobile. (You will add the new CSS styles to global.css later.)

   src/components/Hamburger.astro

   ---
   ---
   <div class="hamburger">
     <span class="line"></span>
     <span class="line"></span>
     <span class="line"></span>
   </div>

3. Place this new <Hamburger /> component just before your <Navigation /> component in Header.astro.

   Show me the code!

   src/components/Header.astro

   ---
   import Hamburger from './Hamburger.astro';
   import Navigation from './Navigation.astro';
   ---
   <header>
     <nav>
       <Hamburger />
       <Navigation />
     </nav>
   </header>

4. Add the following styles for your Hamburger component:

   src/styles/global.css

   /* nav styles */
   .hamburger {
     padding-right: 20px;
     cursor: pointer;
   }
   
   .hamburger .line {
     display: block;
     width: 40px;
     height: 5px;
     margin-bottom: 10px;
     background-color: #ff9776;
   }
   
   .nav-links {
     width: 100%;
     top: 5rem;
     left: 48px;
     background-color: #ff9776;
     display: none;
     margin: 0;
   }
   
   .nav-links a {
     display: block;
     text-align: center;
     padding: 10px 0;
     text-decoration: none;
     font-size: 1.2rem;
     font-weight: bold;
     text-transform: uppercase;
   }
   
   .nav-links a:hover, a:focus {
     background-color: #ff9776;
   }
   
   .expanded {
     display: unset;
   }
   
   @media screen and (min-width: 636px) {
     .nav-links {
       margin-left: 5em;
       display: block;
       position: static;
       width: auto;
       background: none;
     }
   
     .nav-links a {
       display: inline-block;
       padding: 15px 20px;
     }
   
     .hamburger {
       display: none;
     }
   }

Write your first script tag

Section titled Write your first script tag

Your header is not yet interactive because it can’t respond to user input, like clicking on the hamburger menu to show or hide the navigation links.

Adding a <script> tag provides client-side JavaScript to “listen” for a user event and then respond accordingly.

1. Add the following <script> tag to index.astro, just before the closing </body> tag.

   src/pages/index.astro

     <Footer />
     <script>
       document.querySelector('.hamburger').addEventListener('click', () => {
         document.querySelector('.nav-links').classList.toggle('expanded');
       });
     </script>
   </body>

2. Check your browser preview again at various sizes, and verify that you have a working navigation menu that is both responsive to screen size and responds to user input on this page.

Importing a .js file

Section titled Importing a .js file

Instead of writing your JavaScript directly on each page, you can move the contents of your <script> tag into its own .js file in your project.

1. Create src/scripts/menu.js (you will have to create a new /scripts/ folder) and move your JavaScript into it.

   src/scripts/menu.js

   document.querySelector('.hamburger').addEventListener('click', () => {
     document.querySelector('.nav-links').classList.toggle('expanded');
   });

2. Replace the contents of the <script> tag on index.astro with the following file import:

   src/pages/index.astro

     <Footer />
     <script>
       document.querySelector('.hamburger').addEventListener('click', () => {
         document.querySelector('.nav-links').classList.toggle('expanded');
       });
   
       import "../scripts/menu.js";
     </script>
   </body>

3. Check your browser preview again at a smaller size and verify that the hamburger menu still opens and closes your navigation links.

4. Add the same <script> with import to your other two pages, about.astro and blog.astro and verify that you have a responsive, interactive header on each page.

   src/pages/about.astro & src/pages/blog.astro

     <Footer />
     <script>
       import "../scripts/menu.js";
     </script>
   </body>

Takeaway

You had previously used some JavaScript to build parts of your site:

• Defining your page title and heading dynamically
• Mapping through a list of skills on the About page
• Conditionally displaying HTML elements

Those commands are all executed at build time to create static HTML for your site, and then the code is “thrown away.”

The JavaScript in a <script> tag is sent to the browser, and is available to run, based on user interactions like refreshing a page or toggling an input.

Test your knowledge

Section titled Test your knowledge

1. When does Astro run any JavaScript written in a component’s frontmatter?

   1. Astro never runs JavaScript

   2. at build-time

   3. When a visitor clicks a button

   送出

2. Optionally, Astro can send JavaScript to the browser to allow:

   1. users to click page links

   2. faster load times

   3. client-side interactivity

   送出

3. The client-side JavaScript will be sent to a user’s browser when it is written or imported:

   1. in <script> tags

   2. between a .astro file’s code fences

   3. in global.css

   送出

Checklist

Section titled Checklist

• I can add client-side interactivity with JavaScript in a <script> tag.
• I can import a .js file into a <script> tag.

Resources

Section titled Resources

Client-side scripts in Astro