jQuery uses children to find child elements of a specific element

jQuery is a JavaScript library that simplifies common tasks such as HTML document traversal and manipulation, event processing, animation, and AJAX, and the children() method is one of them. children() is a built-in method in jQuery that is used to find all child elements related to the selected element. The children() method in jQuery goes down to a single level of the selected element and returns all elements. In this article, we will gain an in-depth understanding of jQuery's children() method from multiple aspects.

Definition and usage

The children() method returns all direct child elements of the selected element.

DOM tree:This method only traverses a single level down the DOM tree. To traverse multiple levels downwards (return to descendants or other descendants), use the find() method.

hint:To traverse a single level up along the DOM tree, or up to all paths of the document root element (returning to the parent node or other ancestor), use the parent() or parents() method.

Notice:This method does not return a text node. To return all child nodes containing text nodes, use the contents() method.

grammar

$(selector).children(filter)

Selector syntax

$('parentSelector').children(childSelector);

The parameters of the children() method are the selector syntax, and childrenSelector serves as the child element selector of the selected element. In this way, we can use the children() method to select any child elements that meet the criteria. Here are some examples:

1. Select the element with .id as 'child'

$('div').children('#child');

2. Select the element with .class as 'child'

$('div').children('.child');

3. Select all child elements

$('div').children('*');

Chained call

jQuery provides a simple and easy-to-understand chain operation method, and you can directly follow the children() method and other jQuery methods, as shown below:

$('div').children('.child').css({"color": "red", "font-size": "20px"});

The above code will change the font color of all elements in the div with class 'child' to red and resize the font size to 20px.

Return value

The children() method returns all direct child elements of the selected element, excluding all other elements under the child element. Here is a chestnut:

<div class="parent">
  <div class="child"></div>
  <ul>
    <li></li>
    <li></li>
    <li>
      <div class="child"></div>
    </li>
  </ul>
</div>

$('').children();

Execute the above code, the return value will only contain the div element with class 'child', the ul element and all its child elements are not included in the return value.

Performance optimization

When using jQuery's children() method, we need to pay attention to efficiency issues. The children() method is to find all the child elements of the current element from the page, which may cause some performance issues. Considering that this kind of problem is easy to cause, we can use the find() method instead of children(), because find() is to find child elements matching the selector from all descendants of an element.

In addition, when using the children() method, we can use chain operations to avoid duplicate DOM queries. All properties and style changes are done in chained calls, which reduces the number of operations on the DOM.

Summarize

The children() method has multiple uses and can easily accomplish multiple tasks with chain calls. In addition to the methods mentioned above, we can also add filters to the parameters of children(), use children() to locate specific child elements, and use each() method to iterate over child elements, etc.

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