<form> Form 1 <input type='text' oninvalid="setCustomValidity('Cusotm Alert 1');" onchange="setCustomValidity('');" placeholder='This input is required' required/> <input type='text' /> <input type='submit' /> </form> <form> Form 2 <input type='text' oninvalid="setCustomValidity('Cusotm Alert 2');" oninput="setCustomValidity('');" placeholder='This input is required' required/> <input type='text' /> <input type='submit' /> </form>