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Introduction to the theme switcher
Introduction to JavaScript3/17
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  • 1. Why is JavaScript necessary?
  • 2. Introduction to the theme switcher
  • 3. Find an element using querySelector
  • 4. Output the element to the console.
  • 5. Let’s remove the class using classList.remove
  • 6. Let’s add a class to the element using classList.add
  • 7. Declare a variable
  • 8. Introduction to the event handler
  • 9. Let’s make it so that the theme is switched when the button is clicked
  • 10. Introduction to classList.toggle
  • 11. Let’s finish our theme switcher
  • 12. Introduction to the textContent property
  • 13. Change the textual content for the element
  • 14. Uncomment the code
  • 15. We retrieve data from the input field using input.value
  • 16. Let’s use concatenation
  • 17. Summary of “Introduction to JavaScript”
Output the element to the console.
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  • Theory
  • Theory
  • Comments

Find an element using querySelector

We switched the theme on the page by manually changing the classes in the HTML. The time has come to do this using JavaScript.

A JavaScript program is a sequence of instructions that tell the browser to take certain actions. We are going to change the classes for the element with the page class, and first of all we need get access to it from the script. How can we do that? Imagine that JavaScript is a very smart dog (don’t tell Muffin that a dog can be considered smart). He knows many commands, including querySelector, which means “find and retrieve an element”:

document.querySelector('selector');

Please note that this instruction consists of two parts. The first part is the object that JavaScript will search inside. The word document indicates the webpage where the script is included. It really doesn’t matter what the name of the HTML file is. In JavaScript it is always a “document”. It is the parent element of any other element on the page.

The second part of the instruction is what needs to be done. It is called the method. The querySelector method looks for a selector.

To tell JavaScript that the instruction is complete, you need to write a semicolon or make a line break. The line break works correctly in most cases, but the semicolon always works. Therefore, it is better to write a semicolon at the end of each instruction.

So, to find the first element with the class page we must write:

document.querySelector('.page');

Include the file on the page where we will write our code, and find the desired element.

Comments

  • index.html
  • style.css
  • script.js
HTML
<!DOCTYPE html> <html lang="en"> <head> <meta charset="utf-8"> <link rel="stylesheet" href="setting.css"> <link rel="stylesheet" href="style.css"> <title>FlashNews!</title> </head> <body class="page light-theme"> <header class="page-header"> <div class="container"> <a class="header-link" href="#">Main page</a> <button class="theme-button" type="button">Change the theme</button> </div> </header> <main class="inner-main"> <div class="container"> <h1 class="inner-heading">Subscribe to our newsletter</h1> <p class="subscription-message">We promise to send you news no more than once a day. We will only send you the most interesting and important stories.</p> <form action="https://echo.htmlacademy.ru/courses" method="post" class="subscription"> <div class="subscription-inner"> <label class="subscription-label" for="subscription-email">email</label> <input type="email" class="subscription-email" placeholder="muffin@flashnews.ru" value="" required id="subscription-email"> </div> <button class="button subscription-button" type="submit">Subscribe</button> </form> <section class="news-list list-tiles-view"> <h2 class="news-list-heading">Or continue reading more news stories.</h2> <article class="new-block"> <img src="img/new-graph.jpg" alt="New library"> <div class="new-block-text"> <h3>New graphics library</h3> <p>Now you can create a dashboard in just a matter of seconds.</p> <time datetime="2019-10-16">October 16, 2019</time> </div> </article> <article class="new-block"> <img src="img/new-robot.jpg" alt="What is going on with robots?"> <div class="new-block-text"> <h3>What is going on with robots?</h3> <p>A lot of interesting things are happening in robotics. This could be a piece of news about the latest developments, but that is not what this is.</p> <time datetime="2019-10-15">October 15, 2019</time> </div> </article> </section> </div> </main> <footer class="page-footer"> <div class="container"> <p>© FlashNews!</p> <a class="footer-logo"> <img src="img/white-logo.svg" alt="FlashNews! portal logo"> </a> </div> </footer> <!-- Add the code here --> </body> </html>
CSS
/* Light theme */ .light-theme { color: #333333; background-color: #eae9f2; } .light-theme .page-header { background-color: #ffffff; box-shadow: 0 2px 2px rgba(0, 0, 0, 0.2); } .light-theme .header-link { color: #6653d9; } .light-theme .header-link::before { background: url("img/arrow-back-light.svg") no-repeat 0 0; } .light-theme .theme-button { color: #6653d9; border: 1px solid #6653d9; } .light-theme .theme-button::before { background-image: url("img/moon-normal.svg"); } .light-theme .theme-button:focus, .light-theme .theme-button:hover { color: #ffffff; background-color: #6653d9; } .light-theme .theme-button:focus::before, .light-theme .theme-button:hover::before { background-image: url("img/moon-hover.svg"); } .light-theme .menu-open { background-color: #ffffff; background-image: url("img/menu-open-light.svg"); } .light-theme .menu-open:focus, .light-theme .menu-open:hover { background-color: #6653d9; background-image: url("img/menu-open-dark.svg"); } .light-theme .menu-close { background-color: #6653d9; } .light-theme .menu-close:focus, .light-theme .menu-close:hover { background-color: #473c8d; } .light-theme .main-menu { background-color: #6653d9; color: #ffffff; } .light-theme .main-menu a:focus, .light-theme .main-menu a:hover { background-color: #473c8d; } .light-theme .news-view button { border: 1px solid #6653d9; color: #6653d9; } .light-theme .news-view button:focus, .light-theme .news-view button:hover, .light-theme .news-view button:active, .light-theme .news-view .view-checked { background-color: #6653d9; color: #ffffff; } .light-theme .news-view .row-view:focus::before, .light-theme .news-view .row-view:hover::before, .light-theme .news-view .row-view:active::before { background-image: url("img/rows-light-checked.svg"); } .light-theme .news-view .tile-view:focus::before, .light-theme .news-view .tile-view:hover::before, .light-theme .news-view .tile-view:active::before { background-image: url("img/tiles-light-checked.svg"); } .light-theme .row-view::before { background-image: url("img/rows-light.svg"); } .light-theme .tile-view::before { background-image: url("img/tiles-light.svg"); } .light-theme .row-view::before { background-image: url("img/rows-light.svg"); } .light-theme .row-view.view-checked::before { background-image: url("img/rows-light-checked.svg"); } .light-theme .tile-view.view-checked::before { background-image: url("img/tiles-light-checked.svg"); } .light-theme .new-block { background-color: #ffffff; box-shadow: 0 1px 4px rgba(0, 0, 0, 0.2); } .light-theme .new-block time { color: #aaaaaa; } .light-theme .cookies-agreement { background-color: #fdeacd; box-shadow: 0 -1px 4px rgba(0, 0, 0, 0.2); } .light-theme .button { background-color: #6653d9; color: #ffffff; } .light-theme .button:focus, .light-theme .button:hover { background-color: #473c8d; } .light-theme .page-footer { background-color: #6653d9; color: #ffffff; } .light-theme .subscription { background-color: #ffffff; box-shadow: 0 1px 4px rgba(0, 0, 0, 0.2); } .light-theme .subscription-message { background-color: #6653d9; color: #eae9f2; } .light-theme .subscription-message::before { background-image: url("img/icon-ok-light.svg"); } .light-theme .subscription-label { color: #6653d9; } .light-theme .subscription-email { border-bottom: 1px solid #6653d9; color: #333333; } /* Dark theme */ .dark-theme { color: #f2f2f2; background-color: #17161a; } .dark-theme .page-header { background-color: #373540; box-shadow: 0 2px 2px rgba(0, 0, 0, 0.6); } .dark-theme .header-link { color: #9484f2; } .dark-theme .header-link::before { background: url("img/arrow-back-dark.svg") no-repeat 0 0; } .dark-theme .theme-button { color: #9484f2; border: 1px solid #9484f2; } .dark-theme .theme-button::before { background-image: url("img/sun-normal.svg"); } .dark-theme .theme-button:focus, .dark-theme .theme-button:hover { color: #17161a; background-color: #9484f2; } .dark-theme .theme-button:focus::before, .dark-theme .theme-button:hover::before { background-image: url("img/sun-hover.svg"); } .dark-theme .menu-open { background-color: #373540; background-image: url("img/menu-open-dark.svg"); } .dark-theme .menu-open:focus, .dark-theme .menu-open:hover { background-color: #473c8d; background-image: url("img/menu-open-dark.svg"); } .dark-theme .menu-close { background-color: #473c8d; } .dark-theme .menu-close:focus, .dark-theme .menu-close:hover { background-color: #6653d9; } .dark-theme .main-menu { background-color: #473c8d; color: #f2f2f2; } .dark-theme .main-menu a:focus, .dark-theme .main-menu a:hover { background-color: #6653d9; } .dark-theme .news-view button { border: 1px solid #9484f2; color: #9484f2; } .dark-theme .news-view button:focus, .dark-theme .news-view button:hover, .dark-theme .news-view button:active, .dark-theme .news-view .view-checked { background-color: #9484f2; color: #17161a; } .dark-theme .news-view .row-view:focus::before, .dark-theme .news-view .row-view:hover::before, .dark-theme .news-view .row-view:active::before { background-image: url("img/rows-dark-checked.svg"); } .dark-theme .news-view .tile-view:focus::before, .dark-theme .news-view .tile-view:hover::before, .dark-theme .news-view .tile-view:active::before { background-image: url("img/tiles-dark-checked.svg"); } .dark-theme .row-view::before { background-image: url("img/rows-dark.svg"); } .dark-theme .tile-view::before { background-image: url("img/tiles-dark.svg"); } .dark-theme .row-view.view-checked::before { background-image: url("img/rows-dark-checked.svg"); } .dark-theme .tile-view.view-checked::before { background-image: url("img/tiles-dark-checked.svg"); } .dark-theme .new-block { background-color: #2a2930; box-shadow: 0 1px 4px rgba(0, 0, 0, 0.6); } .dark-theme .new-block time { color: #888888; } .dark-theme .cookies-agreement { background-color: #473c8d; box-shadow: 0 -1px 4px rgba(0, 0, 0, 0.6); } .dark-theme .button { background-color: #9484f2; color: #17161a; } .dark-theme .button:focus, .dark-theme .button:hover { background-color: #b6aaff; } .dark-theme .page-footer { background-color: #0a0910; color: #f2f2f2; } .dark-theme .subscription { background-color: #2a2930; box-shadow: 0 1px 4px rgba(0, 0, 0, 0.6); } .dark-theme .subscription-message { background-color: #9484f2; color: #17161a; } .dark-theme .subscription-message::before { background-image: url("img/icon-ok-dark.svg"); } .dark-theme .subscription-label { color: #9484f2; } .dark-theme .subscription-email { border-bottom: 1px solid #9484f2; color: #f2f2f2; }
JavaScript

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Console
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    1. Include the script by adding <script src="script.js"></script> to line 62 in index.html.
    2. Switch to the script.js tab in the code editor.
    3. Use querySelector to find the element with the page class: document.querySelector('.page');.

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