JavaScript Form Validation

JavaScript Form Validation

JavaScript can be used to validate data in HTML forms before sending off the content to a server.

Form data that typically are checked by a JavaScript could be:

• has the user left required fields empty?
• has the user entered a valid e-mail address?
• has the user entered a valid date?
• has the user entered text in a numeric field?

Required Fields

·         The function below checks if a field has been left empty. If the field is blank, an alert box alerts a message, the function returns false, and the form will not be submitted:

·         function validateForm()
{
var x=document.forms["myForm"]["fname"].value;
if (x==null || x=="")
  {
  alert("First name must be filled out");
  return false;
  }
}

·         The function above could be called when a form is submitted:

Example

·        

First name:

---

·         E-mail Validation

·         The function below checks if the content has the general syntax of an email.

·         This means that the input data must contain an @ sign and at least one dot (.). Also, the @ must not be the first character of the email address, and the last dot must be present after the @ sign, and minimum 2 characters before the end:

·         function validateForm()
{
var x=document.forms["myForm"]["email"].value;
var atpos=x.indexOf("@");
var dotpos=x.lastIndexOf(".");
if (atpos<1 atpos="atpos" dotpos="dotpos">=x.length)
  {
  alert("Not a valid e-mail address");
  return false;
  }
}

·         The function above could be called when a form is submitted:

Example

·        

Email: