HTMLFormElement.reportValidity() - Web APIs
the htmlformelement.reportvalidity() method returns true if the element's child controls satisfy their validation constraints.
... syntax htmlformelement.reportvalidity() return value boolean example document.forms['myform'].addeventlistener('submit', function() { document.forms['myform'].reportvalidity(); }, false); specifications specification status comment html living standardthe definition of 'htmlformelement.reportvalidity()' in that specification.
... living standard html 5.1the definition of 'htmlformelement.reportvalidity()' in that specification.

Constraint validation - Developer guides
the constraint validation is done in the following ways: by a call to the checkvalidity() or reportvalidity() method of a form-associated dom interface, (htmlinputelement, htmlselectelement, htmlbuttonelement, htmloutputelement or htmltextareaelement), which evaluates the constraints only on this element, allowing a script to get this information.
...(this is typically done by the user-agent when determining which of the css pseudo-classes, :valid or :invalid, applies.) in contrast, the reportvalidity() method reports any constraint failures to the user.
... by a call to the checkvalidity() or reportvalidity() method on the htmlformelement interface.
... calling checkvalidity() is called statically validating the constraints, while calling reportvalidity() or submitting the form is called interactively validating the constraints.

HTMLObjectElement.setCustomValidity - Web APIs
additionally you must call the reportvalidity method on the same element or nothing will happen.
... function validate(inputid) { var input = document.getelementbyid(inputid); var validitystate_object = input.validity; if (validitystate_object.valuemissing) { input.setcustomvalidity('you gotta fill this out, yo!'); input.reportvalidity(); } else if (input.rangeunderflow) { input.setcustomvalidity('we need a higher number!'); input.reportvalidity(); } else if (input.rangeoverflow) { input.setcustomvalidity('thats too high!'); input.reportvalidity(); } else { input.setcustomvalidity(''); input.reportvalidity(); } } it's vital to set the message to an empty string if there are no errors.

HTMLSelectElement - Web APIs
htmlselectelement.reportvalidity() this method reports the problems with the constraints on the element, if any, to the user.
... living standard since the latest snapshot, html5, it adds the autocomplete property and the reportvalidity() method.

Constraint validation API - Web APIs
reportvalidity() htmlformelement method checks the element's value against its constraints and also reports the validity status; if the value is invalid, it fires an invalid event at the element, returns false, and then reports the validity status to the user in whatever way the user agent has available.

HTMLButtonElement - Web APIs
reportvalidity() boolean not supported for reset or button elements.

HTMLFieldSetElement - Web APIs
htmlfieldsetelement.reportvalidity() always returns true because <fieldset> objects are never candidates for constraint validation.

HTMLFormElement - Web APIs
reportvalidity() returns true if the element's child controls satisfy their validation constraints.

HTMLInputElement - Web APIs
reportvalidity() runs the checkvalidity() method, and if it returns false (for an invalid input or no pattern attribute provided), then it reports to the user that the input is invalid in the same manner as if you submitted a form.

HTMLOutputElement - Web APIs
htmloutputelement.reportvalidity() this method reports the problems with the constraints on the element, if any, to the user.

HTMLTextAreaElement - Web APIs
reportvalidity() this method reports the problems with the constraints on the element, if any, to the user.

Index - Web APIs
1677 htmlformelement.reportvalidity() html, htmlformelement, method, reference the htmlformelement.reportvalidity() method returns true if the element's child controls satisfy their validation constraints.

<input>: The Input (Form Input) element - HTML: Hypertext Markup Language
reportvalidity() returns true if the element's value passes validity checks; otherwise, returns false.