JavaScript reading tutorial: from beginner to proficient

JavaScript reading tutorial: from entry to proficiency

With the development of the Internet, JavaScript has become an indispensable part of front-end development. It has powerful reading capabilities and can obtain and process data on web pages to provide users with a richer interactive experience. This article will start with basic knowledge and gradually introduce the reading function of JavaScript, including specific code examples to help readers from entry to proficiency.

1. Get element content

JavaScript can get the element content on the web page through DOM (Document Object Model). DOM is the logical structure of a page, which can be manipulated through JavaScript. The following is a sample code to get the content of the element:

// 通过id获取元素内容
var elementById = document.getElementById('element-id');
console.log(elementById.innerHTML);

// 通过class获取元素内容
var elementsByClass = document.getElementsByClassName('element-class');
for (var i = 0; i < elementsByClass.length; i++) {
    console.log(elementsByClass[i].innerHTML);
}

// 通过标签名获取元素内容
var elementsByTagName = document.getElementsByTagName('div');
for (var i = 0; i < elementsByTagName.length; i++) {
    console.log(elementsByTagName[i].innerHTML);
}

2. Get the content of the input box

In web pages, users usually enter various information, and JavaScript can get the content of the input box. The following is a sample code to obtain the content of the input box:

// 通过id获取输入框内容
var inputById = document.getElementById('input-id').value;
console.log(inputById);

// 通过class获取输入框内容（假设只有一个输入框）
var inputByClass = document.getElementsByClassName('input-class')[0].value;
console.log(inputByClass);

// 通过name获取输入框内容
var inputsByName = document.getElementsByName('input-name');
for (var i = 0; i < inputsByName.length; i++) {
    console.log(inputsByName[i].value);
}

3. Obtain URL parameters

Sometimes, we need to obtain the parameters in the URL for corresponding processing. The following is a sample code for obtaining URL parameters:

// 获取URL参数函数
function getUrlParameter(name) {
    name = name.replace(/[[]/, '\[').replace(/[]]/, '\]');
    var regex = new RegExp('[\?&]' + name + '=([^&#]*)');
    var results = regex.exec(location.search);
    return results === null ? '' : decodeURIComponent(results[1].replace(/+/g, ' '));
}

// 使用示例
var paramValue = getUrlParameter('param');
console.log(paramValue);

4. Obtaining data through AJAX

In web development, we often need to obtain data from the server through AJAX technology. The following is a sample code for obtaining data through AJAX:

// 创建XMLHttpRequest对象
var xhttp = new XMLHttpRequest();
xhttp.onreadystatechange = function() {
    if (this.readyState == 4 && this.status == 200) {
        var data = JSON.parse(this.responseText);
        console.log(data);
    }
};

// 发送请求
xhttp.open('GET', 'https://api.example.com/data', true);
xhttp.send();

Through the above sample code, readers can gradually learn the reading function of JavaScript and master the practical application in various situations. I hope this article can help readers gradually improve from the introductory stage of JavaScript to the proficient level, and lay a solid foundation for future front-end development.

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