CODE EXAMPLE FOR PHP

Check duplicate email using Jquery validation

//html form
<form id="formId" method="post" action="url">
@csrf
<input type="email" id="email" name="email">
<button type="submit">Submit</button>
</form>

//jquery validation to check Duplicate Emails
//Dont't forget to include jqury and jquery.validation files or CDN
<script>
    $("#FormId").validate({
        rules:{
            email: {
                required: true,
                email:true,
                remote: 'check-duplicate-email'
            }
        },
        messages: {
            email: {
                required: "Email is required",
                email: "Valid Email Please",
                remote: "This Email Already Exists"
            }
        }
    });
<script>

//Route
Route::match(['get', 'post'], 'check-duplicate-email', [ControllerName::class, 'checkDuplicateEmail']);

//controller function
public function checkDuplicateEmail(Request $request){
        if($request->ajax()){
            $adminEmail = $request->email;
            $emailCount = ModelName::where('email', $adminEmail)->count();
            if($emailCount>0){
                echo "false";
            } else {
                echo "true";
            }
        }
    }