Input validation for file attachments using JavaScript

You Can View User Feedback To This Tip

We all have learned that for performance reasons, we should perform field input validations using JavaScript if the user fills a form using a web client.

Download this free guide

Download: IT Certifications 101

Inside this exclusive essential guide, our independent experts break down which IT certifications are worth your time and effort, and how to get started obtaining them to further your career— including specific certifications that any cloud or desktop pro should seriously consider.

Start Download

• Corporate E-mail Address:

  You forgot to provide an Email Address.

  This email address doesn’t appear to be valid.

  This email address is already registered. Please login.

  You have exceeded the maximum character limit.

  Please provide a Corporate E-mail Address.

By submitting my Email address I confirm that I have read and accepted the Terms of Use and Declaration of Consent.

By submitting your personal information, you agree that TechTarget and its partners may contact you regarding relevant content, products and special offers.

You also agree that your personal information may be transferred and processed in the United States, and that you have read and agree to the Terms of Use and the Privacy Policy.

To validate the attachment of a file, however, it is a bit more difficult since the file isn't uploaded until the form is submitted. A solution is to validate the value of the HTML input element instead. The standard Notes file upload control generates an HTML input element (type = "file") which takes the absolute path of the file to be uploaded. The following code validates the contents of that element. It can be put into the onSubmit event of the form along with the rest of the field validation functions.

function validateFileUpload () {
for(i=0;i<document.forms[0].elements.length;++i)
 {
  var elem = document.forms[0].elements[i];
  if (elem.type == "file") {
    alert ("Element-Value: " + elem.value);
    if (elem.value == "") {
        alert ("please attach you file");
        return ("");
    }
  }
 }
}

USER FEEDBACK TO THIS TIP

• One of our friends, Lothar Mueller, submitted a code to validate the file upload control. What he checked was for an entry in that control. However, the code he wrote was not efficient. That way you would need to traverse through all the elements on the form. Here is a much simpler way. Go to File Upload Control properties by right clicking on it. Go to the HTML tab and specify an ID such as fileupload. Then use this ID in the validation of the onSubmit event.

  if (document.forms[0].fileupload.value == ""){
  alert ("please attach a file");
  return false;
  }

  —Loks