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Three ways to use 1.<script></script>:
1. Put in <body>
2. Put in
3. Put in an external JS file
2. Three ways of outputting data:
1. Use the document.write () method to write the contents to an HTML document.
2. Use the Window.alert () pop-up warning box.
3. Write to the HTML element using InnerHTML.
1. Use the id attribute 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.
<! DOCTYPE html>"en">" UTF-8"> <title>Demo</title> document.write (Date ()) </script> <button type=" button" onclick=window.alert (" username must not start with a number ") > Logim</button></body><! DOCTYPE html>"en">"UTF-8"> <title>Demo</title>"Demo">HELLO</p> <script>document.getElementById ("Demo"). InnerHTML =Date (); </script> <button type="Button"Onclick=window.alert ("user name must not start with a number") >LOGIN</button></body>
3. The login page prepares:1. Add the error notification box.
2. Write the Html+css file.
4. Set the ID of each INPUT element to define the JavaScript function.
1. Verify user name 6-20-bit
2. Verify password 6-20-bit
5.onclick calls this function.
<script>function MyLogin () {var ouname= document.getElementById ("umane"); 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="BigBox"> <divclass="Box"> class="Input_box">Account:<input id="umane"Type="text"Placeholder="Please enter user name"> </div> <divclass="Input_box">Password:<input id="UPass"Type="Password"Placeholder="Please enter your password"> </div> <div id="Error_box"><br></div> <divclass="Input_box"> <button onclick="MyLogin ()"> Login </button> <button onclick=window.alert ("do you want to cancel login? ") > Cancel </button></div> </div> </div></body>h2{ align:center; }. bigbox{ -webkit-Flex; Display:flex; width:300px; height:250px; Padding-left:100px; Padding-top:50px; Background-Color:cyan; } # input_box{ align:center; margin:500px; Padding-left:500px; } # error_box{ color:hotpink; } body{padding-right:500px; margin-top:100px; padding-left:500px; font-size:16px; padding-bottom:40px; padding-top:40px; Font-family:verdana,arial,helvetica,sans-serif; }JavaScript Basics, Login front-end verification
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