html input change default error message
<input type="text" id="username" required placeholder="Enter Name"
oninvalid="this.setCustomValidity('Enter User Name Here')"
oninput="this.setCustomValidity('')" />
Source: stackoverflow.com
<input type="text" id="username" required placeholder="Enter Name"
oninvalid="this.setCustomValidity('Enter User Name Here')"
oninput="this.setCustomValidity('')" />