Home Web Front-end Front-end Q&A JavaScript uses if to change background color switching

JavaScript uses if to change background color switching

May 12, 2023 pm 02:16 PM

JavaScript is a high-level programming language widely used in web development. Javascript can be used to change the style of a web page, including modifying the color, font, and style of elements. This article will introduce how to use the if statement of Javascript to switch the background color.

1. Preparation

Before using Javascript, you first need to introduce it into the HTML page. Usually, a <script> tag is added to the <head> tag of HTML to introduce the Javascript file. The sample code is as follows: </p><pre class='brush:php;toolbar:false;'>&lt;html&gt; &lt;head&gt; &lt;script src=&quot;https://cdn.bootcdn.net/ajax/libs/jquery/3.5.1/jquery.min.js&quot;&gt;&lt;/script&gt; &lt;script src=&quot;https://cdn.bootcdn.net/ajax/libs/vue/2.6.11/vue.js&quot;&gt;&lt;/script&gt; &lt;script src=&quot;main.js&quot;&gt;&lt;/script&gt; &lt;/head&gt; &lt;body&gt; &lt;div id=&quot;app&quot;&gt; &lt;h1&gt;Hello, world!&lt;/h1&gt; &lt;/div&gt; &lt;/body&gt; &lt;/html&gt;</pre><p> In addition, we also need a page element to display the background color. In this example, we select the body element as the background color display area. The HTML code is as follows: </p><pre class='brush:php;toolbar:false;'>&lt;body&gt; &lt;div id=&quot;app&quot;&gt; &lt;h1&gt;Hello, world!&lt;/h1&gt; &lt;/div&gt; &lt;/body&gt;</pre><p> 2. Javascript implements background color switching</p><p>After introducing Javascript into the HTML page, we can use Javascript to control the style of page elements. In this example, we can use Javascript to modify the background color of the body element. You can use an if statement to switch the background color. </p><p>The sample code is as follows: </p><pre class='brush:php;toolbar:false;'>var body = document.querySelector('body'); if (body.style.backgroundColor === 'white') { body.style.backgroundColor = 'black'; } else { body.style.backgroundColor = 'white'; }</pre><p>Code analysis: </p><p>First, we use document.querySelector('body') to get the body element. This function returns a reference to an element, which can be manipulated using the body in code. </p><p>Then, we use the if statement to determine whether the current background color is white. If the current background color is white, set the background color to black; otherwise, set the background color to white. </p><p>3. Use the button to trigger the background color switching</p><p>Now, we have implemented the background color switching through the if statement of Javascript. However, if the user wants to switch the background color more conveniently, we can add a button to trigger the switching of the background color. This can be achieved by adding a button element contained in the HTML. </p><p>HTML sample code is as follows: </p><pre class='brush:php;toolbar:false;'>&lt;button onclick=&quot;toggleBackground()&quot;&gt;Click me!&lt;/button&gt;</pre><p>We added a button element and used the onclick attribute to specify the function toggleBackground() to be called when the button is clicked. </p><p>We need to add a function named toggleBackground(), the code is as follows: </p><pre class='brush:php;toolbar:false;'>function toggleBackground() { var body = document.querySelector('body'); if (body.style.backgroundColor === 'white') { body.style.backgroundColor = 'black'; } else { body.style.backgroundColor = 'white'; } }</pre><p>This function is the same as the previous sample code, it uses an if statement to switch the background color. When the button is clicked, this function will be called and the background color will switch to another color. </p><p>4. Complete code implementation</p><p>The following is the complete HTML page code, which can be directly copied to the editor for use. </p><pre class='brush:php;toolbar:false;'> <!DOCTYPE html> <html> <head> <script src="https://cdn.bootcdn.net/ajax/libs/jquery/3.5.1/jquery.min.js"></script> <script> function toggleBackground() { var body = document.querySelector('body'); if (body.style.backgroundColor === 'white') { body.style.backgroundColor = 'black'; } else { body.style.backgroundColor = 'white'; } } </script>

<button onclick="toggleBackground()">Click me!</button>

Hello, world!

In the entire HTML file, we added a

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