Validating data in javascript what is the syntax

Before submitting data to the server, it is important to ensure all required form controls are filled out, in the correct format. This is called client-side form validation , and helps ensure data submitted matches the requirements set forth in the various form controls. This article leads you through basic concepts and examples of client-side form validation. Client-side validation is an initial check and an important feature of good user experience; by catching invalid data on the client-side, the user can fix it straight away. If it gets to the server and is then rejected, a noticeable delay is caused by a round trip to the server and then back to the client-side to tell the user to fix their data. However, client-side validation should not be considered an exhaustive security measure!

It is important to validate the form submitted by the user because it can have inappropriate values. So, validation is must to authenticate user. JavaScript provides facility to validate the form on the client-side so data processing will be faster than server-side validation. Most of the web developers prefer JavaScript form validation.

If a form field fname is empty, this function alerts a message, and returns false, to prevent the form from being submitted:. If a form field fname is empty, the required attribute prevents this form from being submitted:. Server side validation is performed by a web server, after input has been sent to the server.

Forms are ubiquitous in web applications. Some apps use forms to collect data to sign up users and provide an email address. Others use them to fulfill online transactions to facilitate a shopping experience. You might use some web forms to apply for a new car loan, whereas you'll use others to order pizza for dinner. So it's important that the data collected from those forms is cleaned, formatted correctly, and devoid of any malicious code.