Application of dom programming in js: obtaining html elements, js string operations and js number operations-JS Tutorial-php.cn

Home

Web Front-end

JS Tutorial

Application of dom programming in js: obtaining html elements, js string operations and js number operations

不言

Aug 14, 2018 pm 05:09 PM

The content of this article is about the application of DOM programming in js: obtaining html elements, js string operations and js digital operations. It has certain reference value. Friends in need can refer to it. I hope it will help You helped.

DOM Programming:
What is DOM: DOM refers to the structural system of HTML. Our HTML can actually be understood as a tree. Let’s call this tree the DOM model. DOM programming refers to using code to operate the nodes and nodes on this tree. Element,

1. Get html element:
Our html will be considered by js as a document object. js provides many methods for document to obtain html elements and operate html elements:

   <html>
    <head>

        <script>
            function zhanghao() {
                //获取html元素
                var yuansu = document.getElementById("zhangsan2");
                alert(yuansu);
            }        </script>

    </head>

    <body>
        <form>
            账号：<input id="zhanghao1" type="text"><br>
            密码：<input id="zhangsan2" type="password"><br>
            <input type="submit" value="登录"><br>
            <button onclick="zhanghao()"> 获取账号 </button>
        </form>

    </body></html>

Through the program, we found that after changing the method of getting elements, What you get is an HTMLInputElement object, so what is an object. An object is an abstraction of a thing. Abstraction refers to describing a thing through variables. We can access attributes through this object, such as the attributes in the htmlinput object:

function zhanghao() {
                //获取html元素
                var yuansu = document.getElementById("zhanghao1");

                yuansu.style.color = "red";
                yuansu.value= "zhangsan";
            }

Use js to verify whether the account password is empty:

<html>
    <head>

        <script>

            //我们验证账号是否为空， 密码是否为空，如果为空，弹出请输入账号/密码
            function yanzheng() {

                var zhanghao = document.getElementById("zhanghao1").value;                var mima = document.getElementById("zhanghao2").value;                if(zhanghao == &#39;&#39;) {
                    alert("请输入 账号！");
                }   
                if(mima == &#39;&#39;) {
                    alert("请输入密码!");
                }

            }        </script>
    </head>

    <body>
        <form>
            账号：<input  id="zhanghao1" type="text" ><br>
            密码：<input id="zhanghao2" type="password"><br>
            <input type="submit" value="登录"><br>
            <input type="reset" value="重置">
            <a onclick="yanzheng()"> 验证账号密码 </a>
        </form>

    </body></html>

js string operation
Get the string length: By getting the attribute length

//账号的长度必须是6-18位
                var changdu = zhanghao.length;                
                if(6>changdu || changdu > 18) {
                    alert("请输入6-18位的账号！");
                }

字符串常用方法：//常用字符串方法
                var zhanghao = "abcdefg"
                alert(zhanghao.charAt(0)); //根据下标返回对应的字符
                alert(zhanghao.concat("===","++++","&&&&"));//拼接字符串，和+类似
                alert(zhanghao.indexOf("m"));  //判断是否包含某个字符串

                var word="you are SB";
                alert(word.replace("SB","***"));  //替换字符串

                document.write("X" + "1".sub());    //下标
                document.write("X" + "2".sup());    //上标


                var zhanghao = "zhangsan ni hao ";
                document.write(zhanghao.substr(3,4) + "...");  //截取字符串
                document.write(zhanghao.substring(3,4));

js的获取日期：//获取当前操作系统的时间
                var xianzai = new Date();
                document.write(xianzai.toLocaleString());

js mathematical operation: Math

                document.write("<br>");
                document.write(Math.pow(2,3)); 
                document.write("<br>");
                document.write(Math.pow(2,10));
                document.write("<br>");
                document.write(Math.sqrt(2));

                document.write("<br>");
                document.write(Math.random()); //计算随机数

Related recommendations:

Native js pair What operations can be performed on DOM? How to operate DOM with native js

JS Basics DOM and BOM Programming

Javascript & DHTML Example Programming (Tutorial) DOM Basics and Basic API_Basic Knowledge

The above is the detailed content of Application of dom programming in js: obtaining html elements, js string operations and js number operations. For more information, please follow other related articles on the PHP Chinese website!

Statement

The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn

JavaScript in Action: Real-World Examples and ProjectsApr 19, 2025 am 12:13 AM

JavaScript's application in the real world includes front-end and back-end development. 1) Display front-end applications by building a TODO list application, involving DOM operations and event processing. 2) Build RESTfulAPI through Node.js and Express to demonstrate back-end applications.

JavaScript and the Web: Core Functionality and Use CasesApr 18, 2025 am 12:19 AM

The main uses of JavaScript in web development include client interaction, form verification and asynchronous communication. 1) Dynamic content update and user interaction through DOM operations; 2) Client verification is carried out before the user submits data to improve the user experience; 3) Refreshless communication with the server is achieved through AJAX technology.

Understanding the JavaScript Engine: Implementation DetailsApr 17, 2025 am 12:05 AM

Understanding how JavaScript engine works internally is important to developers because it helps write more efficient code and understand performance bottlenecks and optimization strategies. 1) The engine's workflow includes three stages: parsing, compiling and execution; 2) During the execution process, the engine will perform dynamic optimization, such as inline cache and hidden classes; 3) Best practices include avoiding global variables, optimizing loops, using const and lets, and avoiding excessive use of closures.

Python vs. JavaScript: The Learning Curve and Ease of UseApr 16, 2025 am 12:12 AM

Python is more suitable for beginners, with a smooth learning curve and concise syntax; JavaScript is suitable for front-end development, with a steep learning curve and flexible syntax. 1. Python syntax is intuitive and suitable for data science and back-end development. 2. JavaScript is flexible and widely used in front-end and server-side programming.

Python vs. JavaScript: Community, Libraries, and ResourcesApr 15, 2025 am 12:16 AM

Python and JavaScript have their own advantages and disadvantages in terms of community, libraries and resources. 1) The Python community is friendly and suitable for beginners, but the front-end development resources are not as rich as JavaScript. 2) Python is powerful in data science and machine learning libraries, while JavaScript is better in front-end development libraries and frameworks. 3) Both have rich learning resources, but Python is suitable for starting with official documents, while JavaScript is better with MDNWebDocs. The choice should be based on project needs and personal interests.

From C/C to JavaScript: How It All WorksApr 14, 2025 am 12:05 AM

The shift from C/C to JavaScript requires adapting to dynamic typing, garbage collection and asynchronous programming. 1) C/C is a statically typed language that requires manual memory management, while JavaScript is dynamically typed and garbage collection is automatically processed. 2) C/C needs to be compiled into machine code, while JavaScript is an interpreted language. 3) JavaScript introduces concepts such as closures, prototype chains and Promise, which enhances flexibility and asynchronous programming capabilities.

JavaScript Engines: Comparing ImplementationsApr 13, 2025 am 12:05 AM

Different JavaScript engines have different effects when parsing and executing JavaScript code, because the implementation principles and optimization strategies of each engine differ. 1. Lexical analysis: convert source code into lexical unit. 2. Grammar analysis: Generate an abstract syntax tree. 3. Optimization and compilation: Generate machine code through the JIT compiler. 4. Execute: Run the machine code. V8 engine optimizes through instant compilation and hidden class, SpiderMonkey uses a type inference system, resulting in different performance performance on the same code.

Beyond the Browser: JavaScript in the Real WorldApr 12, 2025 am 12:06 AM

JavaScript's applications in the real world include server-side programming, mobile application development and Internet of Things control: 1. Server-side programming is realized through Node.js, suitable for high concurrent request processing. 2. Mobile application development is carried out through ReactNative and supports cross-platform deployment. 3. Used for IoT device control through Johnny-Five library, suitable for hardware interaction.

See all articles