As web developers, we want to protect the information filled out in form fields.Bad information leads to bad user interactions, bad analytics and bad sales. Email addresses should always have the same structure: [email protected] . An email form field should check if the user has entered an email address correctly.Josh also teaches full-stack web development at the UCI Coding Bootcamp.When Josh isn’t building websites, he’s building websites. The value of a text input box (or a textarea or password input) is available using the syntax that tells you which option has been selected.The illustration below shows this relationship: Note that the 'I' in selected Index needs to be capitalised - Java Script functions and variables are always case-sensitive. Read more about the humble checkbox in our HTML5 Checkbox Validation article.User-submitted data should also be verified using a secure server-side script.Otherwise a browser with Java Script disabled, or a hacker trying to compromise your site, can easily by-pass client-side validation.
Using the html attributes we have available as well as some hard-working, built-in Java Script functions, we can do simple client-side form validation.Radio buttons are implemented as if they were an array of checkboxes.