.netcore client-side validation for different onPost handlers (multiple events) - validation

Question

In my .nercore razor page project I have a number of forms with multiple onPost handlers - different buttons for different events (eg. add / copy / edit / delete)
My problem is - I do not understand how I can differentiate client-side validation depending on the button pressed.
EDIT
Let's assume, I have the following .cshtml which defines two input data fields and two buttons. By pressing one button (Add) the first Field A should be validated, by pressing the second (copy) - another one (Field B):
#page "{id:int}/{modeR:int}"
#model MyProject.Pages.MyProjectDB.AddRecordModel
#{
ViewData["Title"] = "Add Record";
}
<div class="row">
<div class="col-md-7">
<form method="post" enctype="multipart/form-data">
<div class="form-group">
<label asp-for="myClass.FieldA" class="control-label"></label>
<input asp-for="myClass.FieldA" class="form-control" />
<span asp-validation-for="myClass.FieldA" class="text-danger"></span>
</div>
<div class="form-group">
<label asp-for="myClass.FieldB" class="control-label"></label>
<input asp-for="myClass.FieldB" class="form-control" />
<span asp-validation-for="myClass.FieldB" class="text-danger"></span>
</div>
<div class="form-group">
<button type="submit" value="Add" class="btn btn-success">Add Record)</button>
<button type="submit" value="Copy" class="btn btn-warning">Edit Record</button>
</div>
</form>
</div>
</div>
#section Scripts {
<partial name="_ValidationScriptsPartial" />
}
at the end of my .cshtml page, but it runs always when onPost is called.
I need to run validation "in groups": for one button set of one fields and ignore others, for another - another set and so on like written above
Is there any way to achieve it without writing custom javascript or do it on server side?..
ANOTHER EDIT
The answer was provided for the case where we have clear separation of input fields / buttons. But how can we handle this if we have two input fields and one button. Validation should NOT be fire if either of them is filled in and should fire if both are null. I understand, this sounds a bit strange, but in my example I have one input field and one dropdown-list. So, either a field should be filled-in or an item should be selected from the list, but for code simplicity let's stay with two input fields (Filed A and Field B, one of them should be filled) and one button:
#page "{id:int}/{modeR:int}"
#model MyProject.Pages.MyProjectDB.AddRecordModel
#{
ViewData["Title"] = "Add Record";
}
<div class="row">
<div class="col-md-7">
<form method="post" enctype="multipart/form-data">
<div class="form-group">
<label asp-for="myClass.FieldA" class="control-label"></label>
<input asp-for="myClass.FieldA" class="form-control" />
<span asp-validation-for="myClass.FieldA" class="text-danger"></span>
</div>
<div class="form-group">
<label asp-for="myClass.FieldB" class="control-label"></label>
<input asp-for="myClass.FieldB" class="form-control" />
<span asp-validation-for="myClass.FieldB" class="text-danger"></span>
</div>
<div class="form-group">
<button type="submit" value="Add" class="btn btn-success">Add Record)</button>
</div>
</form>
</div>
</div>
#section Scripts {
<partial name="_ValidationScriptsPartial" />
}
Thanks in advance!

Answer 1

By pressing one button (Add) the first Field A should be validated, by pressing the second (copy) - another one (Field B) should be validated
You can try to put them in separate <form> and specify handler method via the asp-page-handler attribute, like below.
<h1>Go Add Handler</h1>
<form method="post">
<div class="form-group">
<label asp-for="myClass.FieldA" class="control-label"></label>
<input asp-for="myClass.FieldA" class="form-control" />
<span asp-validation-for="myClass.FieldA" class="text-danger"></span>
</div>
<div>
<button type="submit" value="Add" class="btn btn-success" asp-page-handler="Add">Add Record</button>
</div>
</form>
<hr />
<h1>Go Copy Handler</h1>
<form id="myform" method="post">
<div class="form-group">
<label asp-for="myClass.FieldB" class="control-label"></label>
<input asp-for="myClass.FieldB" class="form-control" />
<span asp-validation-for="myClass.FieldB" class="text-danger"></span>
</div>
<div>
<button type="submit" value="Copy" class="btn btn-warning" asp-page-handler="Copy">Edit Record</button>
</div>
</form>
#section scripts{
#await Html.PartialAsync("_ValidationScriptsPartial")
}
Test Result