<input type="username" class="form-control" name="username" value=""
placeholder="the least 4 character"
data-minlength="4" data-minlength-error="the least 4 character"
data-error="This is a custom Errot Text fot patern and fill blank"
max-length="15" pattern="[A-Za-z0-9]{4,}"
title="4~15 character" required/>
function check(input) {
if(input.validity.typeMismatch){
input.setCustomValidity("Dude '" + input.value + "' is not a valid email. Enter something nice!!");
}
else {
input.setCustomValidity("");
}
}
<input type="text" name="product_title" class="form-control"
required placeholder="Product Name" value="" pattern="([A-z0-9À-ž\s]){2,}"
oninvalid="setCustomValidity('Please enter on Producut Name at least 2 characters long')" />