In-depth understanding of the principles and practical applications of is and where selectors-CSS Tutorial-php.cn

In-depth understanding of the principles and practical applications of is and where selectors

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Release： 2023-09-09 17:54:29

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In-depth understanding of the principles and practical applications of is and where selectors

When using jQuery for DOM operations and event processing, selectors are one of the tools we often use. one. The is and where selectors, especially when dealing with complex DOM structures, can provide us with a more flexible and efficient selection method. This article will deeply explore the principles of is and where selectors, and demonstrate their powerful functions through practical applications.

1. The principle and practical application of the is selector

Principle
The is selector is a method used to match whether a specified selector exists in the element collection. It will traverse the element collection and execute the specified selector to match each element. If the match is successful, it will return true, otherwise it will return false. Since the judgment condition only needs to return true or false, the is selector can end early during execution.
Practical application
(1) Determine whether the element has the specified css class name
```
if($('div').is('.active')) {
 // 执行操作
}
```
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In the above code, the is selector will traverse all div elements and determine whether Has css class named 'active'. If it exists, perform the corresponding operation.

(2) Determine whether the element belongs to the specified selector description

if($('div').is(':visible')) {
    // 执行操作
}

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In the above code, the is selector will traverse all div elements and determine whether they belong to the selection Device description ':visible'. If it belongs, perform the corresponding operation.

2. The principle and practical application of where selector

Principle
The where selector is a method used to filter elements in a collection of elements that meet specified conditions. It will traverse the element collection and execute the specified condition on each element. If the condition is met, the element will be added to the new collection and returned.
Practical application
(1) Filter all elements with specific attributes
```
var result = $('div').where('[data-name]');
// result包含所有具有data-name属性的div元素
```
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In the above code, the where selector will traverse all div elements and filter out those with data- Elements with name attributes, add them to a new collection and return them.

(2) Filter all elements containing the specified text

var result = $('div').where(':contains("Hello")');
// result包含所有包含"Hello"文本的div元素

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In the above code, the where selector will traverse all div elements and filter out the elements containing "Hello" Elements of text, adding them to a new collection returned.

3. Code Example
The following uses a simple example to demonstrate the use of is and where selectors.

<!DOCTYPE html>
<html>
<head>
    <title>jQuery is与where选择器示例</title>
    <script src="https://cdn.jsdelivr.net/npm/jquery@3.5.1/dist/jquery.min.js"></script>
    <script>
        $(document).ready(function(){
            // 判断是否有active类
            if($('div').is('.active')) {
                $('div.active').css('color', 'red');
            }
            
            // 获取所有自定义属性为data-id的元素
            var result = $('div').where('[data-id]');
            console.log(result);
            
            // 获取所有包含'Hello'文本的元素
            var result = $('div').where(':contains("Hello")');
            console.log(result);
        });
    </script>
    <style>
        .active {
            background-color: yellow;
        }
    </style>
</head>
<body>
    <div class="active">Hello, World!</div>
    <div data-id="1"></div>
    <div data-id="2">Hello, jQuery!</div>
    <div>Hello</div>
    <div>World</div>
</body>
</html>

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In the above code, we use the is selector to determine whether there is a div element with the css class name 'active', and set its background color to yellow. Use the where selector to filter div elements with data-id attributes and containing 'Hello' text, and print out the results respectively.

Summary:
Through the introduction of this article, we have an in-depth understanding of the principles and practical applications of the is selector and where selector. Whether it is determining whether an element has a specified CSS class name, filtering elements with specific attributes, or filtering elements that contain specified text, the is and where selectors can play an important role. In actual development, rational use of these two selectors can improve our efficiency and convenience.

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