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JavaScript Basics, Login front-end verification

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    1. Three ways to use <script></script>:
      1. Put in the <body>
      2. Put in the
      3. Placed in an external JS file
    2. Three ways to output data:
      1. Use the document.write () method to write content to an HTML document.
      2. Use the Window.alert () pop-up warning box.
      3. Writes to an HTML element using InnerHTML.
        1. Use the ID property to identify the HTML element.
        2. Use the document.getElementById (ID) method to access HTML elements.
        3. Use innerHTML to get or insert element content.

    3. The login page prepares:
      1. Add an Error prompt box.
      2. Write a good html+css file.
      3. Set the ID of each INPUT element
    4. Defines a JavaScript function.
      1. Verify user name 6-20-bit
      2. Verify password 6-20-bit
    5. The onclick invokes this function.


<! DOCTYPE html>"en">"UTF-8"> <title> time </title> <script type="Text/javascript"Src=".. /static/js2.js"></script>document.write (Date ())</script> <p></p><button type="Button"Onclick=window.alert ("user name cannot start with a number") > Login </button></body>
<! DOCTYPE html>"en">"UTF-8"> <title> Guangzhou Business School </title>"Demo">hello world!</p> <script>document.getElementById ("Demo"). innerhtml=Date (); </script><button type="Button"Onclick=window.alert ("An error occurred on the access page") > Login </button></body></body>
<! DOCTYPE html>"en">"UTF-8"> <title>login</title> <link href=".. /static/css/login.css"Rel="stylesheet"Type="Text/css"> <script>function Fnlogin () {var ouname= document.getElementById ("uname") var oerror= document.getElementById ("Error_box") var oupass= document.getElementById ("UPass")        if(ouname.value.length<6) {oerror.innerhtml="user name is at least 6 bits"        }        if(ouname.value.length>20) {oerror.innerhtml="user name must not exceed 20 digits"        }        if(ouname.value.length>6&ouname.value.length<20&oupass.value.length<6) {oerror.innerhtml="password is at least 6 bits"        }        if(ouname.value.length>6&ouname.value.length<20&oupass.value.length>20) {oerror.innerhtml="password must not exceed 20 digits"        }    }    </script>class="Flex-container"> <divclass="Box"> <div id="Container"style="width:400px"> <div id="Header"style="Background-color:pink"&GT;&LT;H2 align="Center"style="margin-bottom:0;">Login"content"style="Background-color:hotpink;height:150px;width:400px;float:left;"align="Center"> <divclass="Input_box">username:<input id='uname'Type="text"Placeholder="Please input username"></div> <divclass="Input_box">password:<input id='UPass'Type="Password"Placeholder="Please input password"></div><br> <div id="Error_box"><br></div> <divclass="Input_box"> <divclass="Input_box"><button onclick="Fnlogin ()">login</button> <button Onclick=window.alert ("Cancel will not save changes") >cancle</button></div> <div id="Footer"style="Background-color:pink;clear:both;text-align:center;"> duym</div> </div> <br> </div></div></body>
JavaScript Basics, Login front-end verification

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