jQuery iteration function analysis and practical guide

jQuery iterative function analysis and practice guide

In front-end development, the JavaScript library jQuery has been widely used in the realization of web page interaction and dynamic effects. Its powerful selectors and operation functions provide developers with a wealth of tools, making development more efficient and convenient.

In jQuery, iteration is a common operation used to iterate over the elements in a collection and operate on them. This article will provide an in-depth analysis of the commonly used iteration methods in jQuery, and provide practical guidance with specific code examples to help everyone better understand and use the iteration function.

each() method

In jQuery, the each() method is a commonly used iteration method, used to traverse the elements in a collection and perform specified operations on each element. Its basic syntax is:

$(selector).each(function(index, element){
    // 遍历操作
});

Among them, index represents the index of the current element in the collection, and element represents the currently traversed element object. Below we use an example to demonstrate the specific usage of each() method:

// HTML结构
<ul id="list">
    <li>第一项</li>
    <li>第二项</li>
    <li>第三项</li>
</ul>

// JavaScript代码
$("#list li").each(function(index, element){
    console.log("索引：" + index + "，内容：" + $(element).text());
});

In the above example, we use the each() method to traverse the li sub-elements under the ul element with the id of list, and print The index and content of each li element are shown.

map() method

In addition to the each() method, there is also an iterative method map(), which has similar functions but has some differences. The map() method iterates through each element in the collection and creates a new array based on the return value of the callback function. The syntax is as follows:

var newArray = $(selector).map(function(index, element){
    // 返回处理后的数据
});

Below we use an example to demonstrate the usage of the map() method:

// HTML结构
<ul id="list">
    <li>1</li>
    <li>2</li>
    <li>3</li>
</ul>

// JavaScript代码
var newArray = $("#list li").map(function(index, element){
    return parseInt($(element).text()) * 2;
});

console.log(newArray); // 输出 [2, 4, 6]

In the above example, we use the map() method to traverse the list with id The li sub-element under the ul element, and converts the text content in each li element into an integer and then multiplies it by 2, and finally outputs a new array.

Comprehensive application

In addition to each() and map() methods, there are many other iteration methods available, such as filter(), find ()wait. These methods can be used flexibly according to different needs in actual development.

Below we use a comprehensive application example to demonstrate the combined use of multiple iteration methods:

// HTML结构
<ul id="list">
    <li class="item">1</li>
    <li class="item">2</li>
    <li class="item">3</li>
</ul>

// JavaScript代码
var sum = 0;

$("#list li").each(function(index, element){
    if(index % 2 === 0){
        sum += parseInt($(element).text());
    }
});

var filteredArray = $("#list li").map(function(index, element){
    return parseInt($(element).text()) * 2;
}).get();

var filteredItems = $(".item").filter(function(index, element){
    return parseInt($(element).text()) > 2;
});

console.log("偶数索引数字和：" + sum);
console.log("处理后的数组：" + filteredArray);
console.log("大于2的元素：" + filteredItems.length + "个");

In the above example, we calculated the li elements at even index positions through the each() method The sum of the Chinese text content, use the map() method to process the text content of the li element and obtain a new array, use the filter() method to filter out the li elements greater than 2 and print out the number.

Through the above introduction and example demonstration, I believe that everyone has a clearer understanding and mastery of the iteration function in jQuery. In actual development, rational use of iteration methods can make the code more concise and efficient. I hope this article can provide some help for everyone's iterative application in front-end development.

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