Does jquery+ automatically trigger functions?

jQuery is a widely used JavaScript library through which we can easily manipulate HTML documents, handle events, implement animations, and more. The automatic trigger function is programmed to automatically execute a specific function under specified conditions. This article will introduce how to combine jQuery and automatic trigger functions to achieve more efficient and convenient web development.

Let’s first understand the basic syntax of jQuery. When using jQuery, we need to use the $ or jQuery keyword, which are equivalent. For example, to find the element with id foo in an HTML document, you can use the following statement:

$('#foo')  // $符号是jQuery关键字的简写方式

At this time, what is returned is a jQuery object, through which we can perform various operations. For example, you can use the following statement to hide the element:

$('#foo').hide(); // 将id为foo的元素隐藏

jQuery also provides many other methods, such as adding classes, deleting elements, operating CSS properties, etc. You can check the official documentation to learn how to use these methods.

The implementation of the automatic trigger function can be completed by setting a timer (setInterval) or event listening (such as a click event). The following is an example of using setInterval to automatically trigger a function to print Hello World! every second:

setInterval(function() {
    console.log('Hello World!');
}, 1000); // 设置定时器，每1000毫秒执行一次函数

In actual applications, we often need to write automatic trigger functions based on specific business needs. For example, a function is triggered when the user slides the page, or a form is automatically submitted after the user completes input in the input box, etc.

The following is an example implemented using jQuery and an automatic trigger function: when the user slides the page to the bottom, more data is automatically loaded. First, set the function to detect scroll events:

function checkScroll() {
    var documentHeight = $(document).height(); // 文档总高度
    var windowHeight = $(window).height(); // 窗口高度
    var scrollTop = $(window).scrollTop(); // 滚动条距离窗口顶部的距离

    if (documentHeight - scrollTop - windowHeight < 20) {
        // 如果滚动到了底部，执行加载函数
        loadData();
    }
}

Among them, $(document).height() gets the height of the entire document, $(window).height() gets the height of the window, $(window). scrollTop() gets the distance of the scroll bar from the top of the window. If the current scroll reaches the bottom of the page, the function loadData() that loads data is executed.

The following is the specific function for loading data in pages:

var page = 1; // 记录当前页数
function loadData() {
    $.ajax({
        type: 'GET',
        url: 'data.php',
        data: {page: page},
        success: function(data) {
            // 处理从服务器返回的数据
            $('#result').append(data); // 将数据追加到页面上
            page++; // 页面数加一
        }
    });
}

Use jQuery's ajax method to load data asynchronously. Among them, page records the current page number, and page increases by 1 each time data is loaded. After the data is loaded successfully, append the data to the HTML element with the id of result.

Finally, after the page is loaded, use the following code to set up the scroll event listening and automatically load the data when sliding to the bottom:

$(document).ready(function() {
    $(window).scroll(function() {
        checkScroll(); // 滚动时检查是否到底部了
    });
});

When the page is loaded, listen for the scroll event and Check if it slides to the bottom. If you slide to the bottom, the checkScroll() function is executed to automatically load data.

In this way, we can easily implement some common front-end functions, making web development more efficient and convenient. Of course, the above is just a simple example, and there are many details to consider in actual applications, such as throttling and anti-shake of page scrolling, code reusability and maintainability, etc. I hope this article can help readers understand jQuery and automatic trigger functions.

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