1. script

                
  //used in form blades
  $(document).on('click','#btn_save, .btn_save',function(event) {   
    
       
       // var formId= $(this).attr('data-form');
        var formId=  $(this).closest('form').attr('id');
        //var formId=$(this).parent().closest('form');
       
        var ajax_url= $(this).attr('data-ajax_url');
        var beforeAction= $(this).attr('data-beforeAction');
        var afterAction= $(this).attr('data-afterAction');
        var callBackFunction=$(this).attr('data-callBackFunction');
       
      
        
        formValidation(formId, beforeAction, afterAction, ajax_url, callBackFunction); 

  });


 $("#btn_draft").click(function() {
    var formId=  $(this).closest('form').attr('id');
    var ajax_url= $(this).attr('data-ajax_url');
    var beforeAction= $(this).attr('data-beforeAction');
    var afterAction= $(this).attr('data-afterAction');

     $('#mode').val('draft');
     $('.form-control').removeClass('mandatory');
    formValidation(formId, beforeAction, afterAction ,ajax_url); 
});

  var isPostRequest=0;   
  function formValidation(formId, beforeAction='', afterAction='', ajax_url='', callBackFunction=''){
             var error=0;
             var focusStatus=0;
            
           
             if(beforeAction==1){
               // error=doBeforeAction(error);  
               error=eval(doBeforeAction+"(error)");            
             }


            $('#'+formId+' .mandatory').each(function(index, obj){
            // $('.'+formId).children('.mandatory').each(function(index, obj){
                
                switch(obj.type){
                   case 'radio':
                        var length=$("input[name="+obj.name+"]:checked").length;
                        if(length==0){
                            $(obj).parent().next('.errormessage').show();			
                            $(obj).parent().next('.errormessage').text($(obj).data('message')); 
                            error=1;      
                        }
                   break;
                  

                   default:
                        if(obj.value==''){
 
                            console.log($(obj).data('message'));
                            $(obj).parent().find('.errormessage').show();			
                            $(obj).parent().find('.errormessage').text($(obj).data('message')); 
                            if(focusStatus==0){
                                $(obj).focus();
                                focusStatus=1;
                            }
                            
                            error=1;      
                          //return false;              
                          
                        }
                   break;
                }                 
               
                
            });

            //multiselect
            $('#'+formId+' .filter-multi-select').each(function(index, obj){           
                multiItems=$(obj).find('.selected-items .item').length
                if(multiItems==0){
                    $(obj).parent().find('.errormessage').show();	
                    $(obj).parent().find('.errormessage').text('Please select items'); 
                }
            });


            if(afterAction==1){
               //error=doAfterAction(error);  
               error=eval(doAfterAction+"(error)");            
            }

         

            if(error==0){
                $('#overlay1').fadeIn();
                $('#btn_save').prop('disabled', true);
               // $('#btn_save').html('<i class="fa  fa-spinner"></i>&nbsp;Wait');

                $('.btn_save').prop('disabled', true);
                //$('.btn_save').html('<i class="fa  fa-spinner"></i>&nbsp;Wait');

                //block multipe request from popup
                if(isPostRequest==0){
                    isPostRequest=1;
                }
                else{
                    return false;
                }

                if(ajax_url!='' && ajax_url!=undefined){

                            var dataString = $("#"+formId).serialize();
                            $.ajax({
                                type: 'POST',
                                url: ajax_url,
                                headers: {
                                    'X-CSRF-TOKEN': $('meta[name="csrf-token"]').attr('content')
                                },
                
                                data:dataString,
                                dataType: 'json',
                                success:function(response){	
                                    $('#btn_save').prop('disabled', false);
                                    $('.btn_save').prop('disabled', false);
                                    //lastCallBackItem=ajaxCallbackFunction.pop();
                                    console.log(callBackFunction);                                   
                                    eval(callBackFunction+"(response)");

                                    $('#overlay1').fadeOut();
                                    isPostRequest=0;
                                },
                                error: function(xhr, ajaxOptions, thrownError) { // if error occured
                                    response =jQuery.parseJSON(xhr.responseText);											
                                                    
                                }	
                            }); 

                }
                else{
                    //alert(formId);
                    $('#'+formId).submit();
                }
               
            }
            else{
                  // Swal.fire({
                  //     icon: 'warning',
                  //     title: 'Validation Error',
                  //     text: "Please fill all mandatory fields",
                  //     footer: ''
                  // });
                  return false;  
            }
  }

//used in form blades
 $(document).on('focus, keypress, change','.form-control, .form-check-input',function(event) { 
	    $(this).next('.errormessage').hide();
});

2. html

<form id="admin_form_1737186047" class="admin_form" >

<button type="button" class="btn btn-success btn-sm btn_save" id="btn_save" data-form="admin_form"  data-beforeAction="customFunctionBefore"  data-afterAction="customFunctionAfter" data-ajax_url="write you route" data-callBackFunction="customAjaxCallback"><i class="fa fa-save"></i>&nbsp;Save</button>  

function customFunctionBefore(error){

            //write your custom validation
            if(error==1){
                  return 1;
            }

}

function customFunctionAfter(error){
            //write your custom validation
            if(error==1){
                  return 1;
            }
}

function customAjaxCallback(response){
    //write your custom logic
}

1. data-beforeAction & data-afterAction are for custom validation
2. data-ajax_url for ajax form submit
3. data-callBackFunction for callback after ajax call