Understand the usage of jQuery index() method

Introduction

In the process of using jQuery for development, the index() method is often used To get the index position of the specified element in the parent element. The index() method can easily help developers operate and locate elements, improving the flexibility and efficiency of the code.

index() method overview

The index() method is a common method in jQuery, used to obtain the index position of a specified element relative to its sibling elements. The basic syntax of this method is:

$(selector).index()

where selector is the element selector to get the index value.

Example 1: Basic usage

Suppose there is an HTML structure as follows:

  
第一个元素
  
第二个元素
  
目标元素
  
第四个元素

If you want to get the index of the li element with the id "target" in its sibling element Position, you can use the following code:

var index = $('#target').index();
console.log(index); // 输出：2

In the above code, the result returned by the index() method is the index position of the target element in the sibling element, counting from 0.

Example 2: Combining parent elements

Sometimes, you need to get the index position of the target element in all child elements under its parent element. For example, if we have the following HTML structure:

  
第一个元素
  
第二个元素
  
目标元素
  
第四个元素

To get the index position of the li element with the id "target" among all child elements under its parent element ul, you can use the following code:

var index = $('#target').index('ul li');
console.log(index); // 输出：2

In this example, the index() method accepts a parameter indicating the child elements under the parent element to be searched. The index position of the target element under the specified parent element will be calculated.

Example 3: Filtering elements

Sometimes, we may only obtain the index position of elements under certain conditions. The following is an example, assuming the following HTML structure:

  
第一个元素
  
第二个元素
  
目标元素
  
第四个元素

If you only want to get the index position of the element with class "item" among its sibling elements, you can add a selector parameter:

var index = $('#target').index('.item');
console.log(index); // 输出：2

In this example, the index() method will only calculate the index position of the element with class "item" among its sibling elements.

Conclusion

Through the introduction and examples of this article, we understand the basic usage of the jQuery index() method. This method is very helpful in obtaining the flexibility and efficiency of elements at specified positions, and can easily help developers position and operate elements. Hope this article helps you understand the jQuery index() method!

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