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

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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:

   
    

        

    

    
        

            账号：

            密码：

            

             获取账号 
        

    

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:

    

        
    

    
        

            账号：

            密码：

            

            
             验证账号密码 
        

    

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

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

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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

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