What are the common uses of id selectors?

The id selector is commonly used in page internal link anchors, JavaScript operation elements, style control and form validation. Detailed introduction: 1. Page internal link anchors. ID selectors are often used in page internal link anchors. By setting a unique ID on the target element, you can create links elsewhere in the page so that users can jump directly. Go to the location of the target element; 2. JavaScript operates elements. ID selectors are often used in JavaScript to operate HTML elements, etc.

The operating system for this tutorial: Windows 10 system, DELL G3 computer.

The ID selector is one of the most commonly used selectors in CSS and is used to select HTML elements with a specified ID. The ID selector selects elements by setting a unique ID attribute to the element. The following are common applications of ID selectors:

1. Page internal link anchors:

ID selectors are often used in page internal link anchors. By setting a unique ID on the target element, you can create links elsewhere on the page so users can jump directly to where the target element is.

<h2 id="section1">Section 1</h2>
   <p>Content of section 1</p>
   <a href="#section1">Go to Section 1</a>

In the above example, the ID selector is used to create an internal link on the page. When the user clicks the "Go to Section 1" link, the page will scroll to the element with the ID "section1".

2. JavaScript operating elements:

ID selectors are often used to operate HTML elements in JavaScript. By using the getElementById() method, the corresponding DOM element can be obtained according to the element's ID, so that it can be operated, modified, or event listeners added.

   var element = document.getElementById("myElement");
   element.style.color = "red";

In the above example, the element with the ID "myElement" is obtained through the ID selector and its text color is set to red.

3. Style control:

The ID selector can be used to apply styles to elements with specific IDs. By setting the ID attribute for an element and using the corresponding ID selector in CSS, you can control the style of the element.

   <p id="highlight">This paragraph is highlighted.</p>

   #highlight {
     background-color: yellow;
   }

In the above example, the ID selector is used to select the paragraph element with the ID "highlight" and set its background color to yellow to achieve the highlight effect.

4. Form validation:

ID selectors are also often used in form validation. By setting the ID attribute for the form element and using the ID selector in JavaScript to obtain the corresponding form element, the data entered by the user can be verified, processed, and submitted.

   <form id="myForm">
     <input type="text" id="username" required>
     <input type="password" id="password" required>
     <button type="submit">Submit</button>
   </form>

   var form = document.getElementById("myForm");
   form.addEventListener("submit", function(event) {
     event.preventDefault();
     // 表单验证和处理逻辑
   });

In the above example, the ID selector is used to obtain the form element with the ID "myForm", and a listener for the form submission event is added.

It should be noted that the ID selector should remain unique, and each ID can only be used once in the page. Otherwise, it may result in incorrect selector matching or style conflicts.

In summary, ID selectors are widely used in page internal link anchors, JavaScript operation elements, style control and form validation. Reasonable use of ID selectors can improve the readability and maintainability of code, and also provide developers with richer style control and interactive capabilities.

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