or
, it can be very useful in certain situations.
- Using the selector
In CSS, the selector represents the currently selected element. For example, if we want the background color of the clicked element to turn red, we can do it in the following way:
<code><style>
this:active {
background-color: red;
}
</style></code>
In this way, when the user clicks on an element, will be automatically applied to this element.
- Use to refer to the current element
In JavaScript, can be used as a keyword to refer to the element currently executing the script. For example, consider the following HTML code:
<code><button onclick="alert(this.innerText)">Click me</button></code>
In this example, when the user clicks on the "Click me" button, an alert box pops up showing the text content of the button. This is because we use the keyword to reference the current button element, so that the text content of the button can be obtained and displayed when the script is executed.
- Use to reference parent elements
In addition to referencing the current element, can also be used in JavaScript to reference its parent element. For example, consider the following HTML code:
<code><div onclick="alert(this.parentNode.tagName)">Click me</div></code>
In this example, when the user clicks on the
element, an alert box pops up showing the tag name of the
's parent element. This is because we use the
keyword to reference the current element, then get its parent element through the parentNode attribute, and finally get and display its tag name.
- Use for form validation
In HTML, can be used for form validation and control the submission of the form based on the validation results. . For example, consider the following HTML code:
<code><form onsubmit="return validateForm(this);">
<input type="text" name="name"/>
<input type="submit" value="Submit"/>
</form></code>
In this example, we use the keyword to reference the current form element and pass it as a parameter to the validateForm() function. This function will validate the "name" field of the form and decide whether the form can be submitted based on the validation result. If the verification fails, return false to prevent form submission; otherwise, return true to allow form submission.
Conclusion
Although the element is used relatively rarely in HTML, it plays a very important role in CSS and JavaScript. By understanding the usage of , we can better grasp the basic syntax of HTML, CSS and JavaScript, so as to design and develop web pages more efficiently.
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