A simple example of determining whether the value entered by the user is empty in js

Author：Eve Cole Update Time：2025-03-23 05:16:01

Determining whether the value entered by the user is empty in js is something that everyone uses a lot. There is nothing to write about. But I did it. The reason is just that I think my code is well written, for your reference. one time.

This is taken from the user registration page of one of my projects. For most people, this is almost 100% experienced.

Post the code, these codes are all written in js. It is not difficult and easy to understand. When reading, you only need to distinguish between the two js classes.

Front page code: reguser.aspx

Copy the code code as follows:

<%@ Page language="c#" Codebehind="RegUser.aspx.cs" AutoEventWireup="false" Inherits="Enterprise.Web.RegUser" %>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" >

<html>

<head>

<title>User Registration</title>

var reg = {};

reg.userName = '';

reg.password = '';

reg.confirmPassword = '';

reg.question = '';

reg.answer = '';

reg.url = '';

reg.sex = 1;

reg.email = '';

reg.tel = '';

reg.mobile = '';

reg.qq = '';

reg.address = '';

reg.postalcode = '';

reg.form = null;

function btnSubmit_onclick()

{

reg.form = document.forms[0];

var comFun = new commonFunction();

if(!comFun.checkIsEmpty(reg.form))

{

return false;

}

if(comFun.$getElementById('txtPassword').value!=comFun.$getElementById('txtConfirmPassword').value)

{

alert('The two password inputs are inconsistent');

comFun.$getElementById('txtConfirmPassword').select();

return false;

}

reg.userName = comFun.$getElementById('txtUserName');

reg.password = comFun.$getElementById('txtPassword');

reg.question = comFun.$getElementById('txtQuestion');

reg.answer = comFun.$getElementById('txtAnswer');

reg.url = comFun.$getElementById('txtUrl');

reg.email = comFun.$getElementById('txtEmail');

reg.tel = comFun.$getElementById('txtTel');

reg.mobile = comFun.$getElementById('txtMobile');

reg.qq = comFun.$getElementById('txtQQ');

reg.address = comFun.$getElementById('txtAddress');

reg.postalcode = comFun.$getElementById('txtPostalcode');

var es = comFun.$getElementsByName('sex');

var eL = es.length;

for(var i=0; i<eL; i++)

{

var e = es[i];

if(e.checked)

{

reg.sex = e.value;

break;

}

RegUser.Reg(reg.userName.value, reg.password.value, reg.question.value, reg.answer.value, reg.url.value, reg.sex.value, reg.email.value, reg.tel. value, reg.mobile.value, reg.qq.value, reg.address.value, reg.postalcode.value, callback_Reg);

}

function callback_Reg(res)

{

var rv = res.value;

if(rv)

{

alert('Registration successful!');

window.location.href='/Default.aspx';

}

else

{

alert('An error occurred and registration failed! It is possible that the username or domain name has been registered by someone else!');

}

// Check whether the domain name of the user name has been registered by other users

function checkIsRegistered(obj, errorS, t)

{

var v = obj.value;

var rv = RegUser.CheckIsRegistered(v, t).value;

if(rv)

{

alert(errorS);

obj.select();

return false;

}

</script>

</head>

<tr>

<td><div align="right">Username:</div>

</td>

</tr>

<tr>

<td><div align="right">Password:</div>

</td>

</tr>

<tr>

<td><div align="right">Confirm password:</div>

</td>

</tr>

<tr>

<td><div align="right">Password question:</div>

</td>

</tr>

<tr>

<td><div align="right">Password question answer:</div>

</td>

</tr>

<tr>

<td><div align="right">SiteUrl:</div>

</td>

</tr>

<tr>

<td><div align="right">Gender:</div>

</td>

<td><input type="radio" id="boy" name="sex" value="1" checked>Male<input type="radio" id="girl" name="sex" value="0" >Female</td>

</tr>

<tr>

<td><div align="right">Email:</div>

</td>

</tr>

<tr>

<td><div align="right">Landline:</div>

</td>

</tr>

<tr>

<td><div align="right">Mobile phone:</div>

</td>

</tr>

<tr>

</td>

</tr>

<tr>

<td><div align="right">Address:</div>

</td>

</tr>

<tr>

</td>

</tr>

<tr>

<td><div align="right">Operation:</div>

</td>

</tr>

</table>

</form>

</body>

</html>

In the above code, a CommonFunction.js file is included. Here is its content:

Copy the code code as follows:

/************************************************ **********

* Public js function

*************************************************** *********/

function commonFunction()

{

// check value is null or empty

this.checkIsEmpty = function(obj)

{

var flag = true;

for(var i=0; i<obj.length; i++)

{

var e = obj.item(i);

if(e.isRequired)

{

if(e.value=='')

{

alert(e.errorSForEmpty);

e.focus();

flag = false;

break;

}

if(e.isValidate)

{

if(this.checkValidate(e)==false)

{

alert(e.errorSForValidate);

e.select();

e.focus();

flag = false;

break;

}

return flag;

}

// check value is validated

this.checkValidate = function(e)

{

var v = e.value;

if(v!='')

{

return this.checkReg(e.validatePattern, v);

}

// regexp validate

this.checkReg = function(pattern, value)

{

pattern = pattern.substring(1, pattern.length-1);

var reg = new RegExp(pattern);

if(!reg.test(value))

{

return false;

}

// return an Element By id object for what id.

this.$getElementById = function(id)

{

var e = document.getElementById(id);

if(e!='undefined')

{

return e;

}

return;

}

// return an Element By name object for what id.

this.$getElementsByName = function(id)

{

var e = document.getElementsByName(id);

if(e!='undefined')

{

return e;

}

return;

}

Post a picture of the effect: