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Build robust forms with built-in HTML5 validation and custom JavaScript validation.
HTML5 introduced powerful built-in form validation that works without JavaScript. Attributes like required, pattern, min, max, minlength, and maxlength provide instant feedback to users.
Input types like email, url, number, and date come with built-in validation. The browser automatically checks that the input matches the expected format before allowing submission.
For custom validation, use the setCustomValidity() method and the constraint validation API. You can listen to the invalid event to show custom error messages.
JavaScript validation provides the most flexibility. Validate on input for real-time feedback, on blur for field-level validation, and on submit for final checks. Always validate on the server too — client-side validation is for UX, not security.
Build and test forms in CompileZ's HTML editor. Try the form tutorial to see validation in action.
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