Does jquery have before?-Front-end Q&A-php.cn

Does jquery have before?

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Release： 2023-05-12 09:43:36

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jQuery is a very popular JavaScript library that provides many convenient methods and functions that can help us more easily manipulate and manage components on HTML documents and web pages. In jQuery, there are many commonly used functions, including the before() function. So, what exactly is before()? What does it do? In this article, we will answer these questions one by one.

`before()` Basic syntax of the function

In jQuery, we can use the before() function to insert new content before the element . Its basic syntax is as follows:

$(selector).before(content);

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where selector is the selector expression of the element before which content is to be inserted, and content is the content to be inserted. content can be HTML code, text, or a jQuery object.

`before()` Function of the function

Using the before() function, we can insert new content anywhere on the page. For example, suppose we have the following HTML code:

<div id="myDiv">
  <p>Hello World!</p>
</div>

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We can use the before() function to insert a new piece of HTML code before this <div> element , as shown below:

$("#myDiv").before("<h1>Welcome</h1>");

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This will insert a new <h1> element before the myDiv element, and the result of the page will be as follows:

<h1>Welcome
<div id="myDiv">
  <p>Hello World!</p>
</div>

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We can also move an existing element to another position through the before() function. For example, suppose we have the following HTML code:

<div>
  <p>Paragraph 1</p>
  <p>Paragraph 2</p>
</div>

<div id="newDiv"></div>

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We can use the before() function and the selector to move the second  element to #newDiv element, as shown below:

$("#newDiv").before($("div:first p:last"));

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The final HTML code will be like this:

<div id="newDiv">
  <p>Paragraph 2</p>
</div>

<div>
  <p>Paragraph 1</p>
</div>

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With the above code, we successfully added the second  The element is moved before the #newDiv element.

`before()` Chained use of functions

jQuery can use chained operations, which also means that before() can be used multiple times function. For example, suppose we have the following HTML code:

<div id="myDiv">
  <p>Paragraph 1</p>
  <p>Paragraph 2</p>
</div>

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We can insert three new  elements before the #myDiv element using the following code, As shown below:

$("#myDiv")
  .before("<p>New Paragraph 1</p>")
  .before("<p>New Paragraph 2</p>")
  .before("<p>New Paragraph 3</p>");

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The final HTML code will be like this:

<p>New Paragraph 3
<p>New Paragraph 2
<p>New Paragraph 1
<div id="myDiv">
  <p>Paragraph 1</p>
  <p>Paragraph 2</p>
</div>

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`before()` function and `insertBefore()` function Comparison

In jQuery, the before() function works very similarly to the JavaScript native insertBefore() function. So, what's the difference between the two?

First of all, insertBefore() is a native JavaScript function, and before() is a function provided by jQuery. This means that the insertBefore() function is more flexible than the before() function and can be used in native JavaScript code. On the other hand, the before() function is more convenient than the insertBefore() function and can be called multiple times using chained operations.

Secondly, their parameter order is different. insertBefore() The syntax of the function is:

parentElement.insertBefore(newElement, referenceElement);

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Among them, parentElement is the parent element into which the new element is to be inserted, and newElement is The new element to be inserted, referenceElement is the reference element before which the new element is to be inserted.

Comparisonbefore() Function syntax:

$(referenceElement).before(newElement);

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Among them, referenceElement is the existing element and newElement is the The new element inserted.

Finally, the before() function returns the jQuery object containing the new element, while the insertBefore() function returns the new element itself.

Conclusion

Through the introduction of this article, we understand the usage and function of the before() function in jQuery. We can use the before() function to insert new content at any position, or move an existing element to another position through a selector. We also showed that the before() function can be used to chain operations to insert multiple new elements.

Compared with the native JavaScript function insertBefore(), the before() function is more convenient and slightly less flexible.

When using it, we should choose specific functions based on actual needs. Whether using before() or insertBefore(), they are very useful tools that can help us manage and manipulate elements on the web page more easily.

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