jQuery validation: change default error message

You can specify your own messages in the validate call. Lifting and abbreviating this code from the Remember the Milk signup form used in the Validation plugin documentation (http://jquery.bassistance.de/validate/demo/milk/), you can easily specify your own messages:

var validator = $("#signupform").validate({
    rules: {
        firstname: "required",
        lastname: "required",
        username: {
            required: true,
            minlength: 2,
            remote: "users.php"
        }
    },
    messages: {
        firstname: "Enter your firstname",
        lastname: "Enter your lastname",
        username: {
            required: "Enter a username",
            minlength: jQuery.format("Enter at least {0} characters"),
            remote: jQuery.format("{0} is already in use")
        }
    }
});

The complete API for validate(...) : http://jqueryvalidation.org/validate

This worked for me:

$.validator.messages.required = 'required';

This worked for me:

// Change default JQuery validation Messages.
$("#addnewcadidateform").validate({
        rules: {
            firstname: "required",
            lastname: "required",
            email: "required email",
        },
        messages: {
            firstname: "Enter your First Name",
            lastname: "Enter your Last Name",
            email: {
                required: "Enter your Email",
                email: "Please enter a valid email address.",
            }
        }
    })

Since we're already using JQuery, we can let page designers add custom messages to the markup rather than the code:

<input ... data-msg-required="my message" ...

Or, a more general solution using a single short data-msg attribute on all fields:

<form id="form1">
    <input type="text" id="firstName" name="firstName" 
        data-msg="Please enter your first name" />
    <br />
    <input type="text" id="lastName" name="lastName" 
        data-msg="Please enter your last name" />
    <br />
    <input type="submit" />
</form>

And the code then contains something like this:

function getMsg(selector) {
    return $(selector).attr('data-msg');
}

$('#form1').validate({
    // ...
    messages: {
        firstName: getMsg('#firstName'),
        lastName: getMsg('#lastName')
    }
    // ...
});

Another possible solution is to loop over the fields, adding the same error message to each field.

$('.required').each(function(index) {
  $(this).rules("add", {
    messages: {
      required: "Custom error message."
   }
  });
});

Instead of changing the plugin source code you can include an additional js file in the format like those in the downloads localization folder and include that one after loading the validation.js

jQuery.extend(jQuery.validator.messages, {
    required: ...,
    maxlength: jQuery.validator.format(...),
    ...
});

The newest version has some nice in-line stuff you can do.

If it's a simple input field you can add the attribute data-validation-error-msg like this --

data-validation-error-msg="Invalid Regex"

If you need something a little heavier you can fully customize things using a variable with all the values which is passed into the validate function. Reference this link for full details -- https://github.com/victorjonsson/jQuery-Form-Validator#fully-customizable

@Josh: You can expand your solution with translated Message from your resource bundle

<script type="text/javascript">
    $.validator.messages.number = '@Html.Raw(@Resources.General.ErrorMessageNotANumber)';
</script>

If you put this code part into your _Layout.cshtml (MVC) it's available for all your views

I never thought this would be so easy , I was working on a project to handle such validation.

The below answer will of great help to one who want to change validation message without much effort.

The below approaches uses the "Placeholder name" in place of "This Field".

You can easily modify things

   // Jquery Validation   
   $('.js-validation').each(function(){

       //Validation Error Messages 

       var validationObjectArray = [];

       var validationMessages = {};

       $(this).find('input,select').each(function(){  // add more type hear

          var singleElementMessages = {};

          var fieldName = $(this).attr('name');

          if(!fieldName){  //field Name is not defined continue ;
              return true;
          }


          // If attr data-error-field-name is given give it a priority , and then to placeholder and lastly a simple text

          var fieldPlaceholderName = $(this).data('error-field-name') || $(this).attr('placeholder') || "This Field";

          if( $( this ).prop( 'required' )){

              singleElementMessages['required'] = $(this).data('error-required-message') || $(this).data('error-message')  || fieldPlaceholderName + " is required";

          }

          if( $( this ).attr( 'type' ) == 'email' ){

              singleElementMessages['email'] = $(this).data('error-email-message') || $(this).data('error-message')  || "Enter valid email in "+fieldPlaceholderName;

          }       



          validationMessages[fieldName] = singleElementMessages;

       });


       $(this).validate({
          errorClass   : "error-message",
          errorElement : "div",
          messages     : validationMessages  
       });  
   });  

To remove all default error messages use

$.validator.messages.required = "";

$(function() {

$("#username_error_message").hide();
$("#password_error_message").hide();
$("#retype_password_error_message").hide();
$("#email_error_message").hide();

var error_username = false;
var error_password = false;
var error_retype_password = false;
var error_email = false;

$("#form_username").focusout(function() {

    check_username();
    
});

$("#form_password").focusout(function() {

    check_password();
    
});

$("#form_retype_password").focusout(function() {

    check_retype_password();
    
});

$("#form_email").focusout(function() {

    check_email();
    
});

function check_username() {

    var username_length = $("#form_username").val().length;
    
    if(username_length < 5 || username_length > 20) {
        $("#username_error_message").html("Should be between 5-20 characters");
        $("#username_error_message").show();
        error_username = true;
    } else {
        $("#username_error_message").hide();
    }

}

function check_password() {

    var password_length = $("#form_password").val().length;
    
    if(password_length < 8) {
        $("#password_error_message").html("At least 8 characters");
        $("#password_error_message").show();
        error_password = true;
    } else {
        $("#password_error_message").hide();
    }

}

function check_retype_password() {

    var password = $("#form_password").val();
    var retype_password = $("#form_retype_password").val();
    
    if(password !=  retype_password) {
        $("#retype_password_error_message").html("Passwords don't match");
        $("#retype_password_error_message").show();
        error_retype_password = true;
    } else {
        $("#retype_password_error_message").hide();
    }

}

function check_email() {

    var pattern = new RegExp(/^[+a-zA-Z0-9._-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,4}$/i);

    if(pattern.test($("#form_email").val())) {
        $("#email_error_message").hide();
    } else {
        $("#email_error_message").html("Invalid email address");
        $("#email_error_message").show();
        error_email = true;
    }

}

$("#registration_form").submit(function() {
                                        
    error_username = false;
    error_password = false;
    error_retype_password = false;
    error_email = false;
                                        
    check_username();
    check_password();
    check_retype_password();
    check_email();
    
    if(error_username == false && error_password == false && error_retype_password == false && error_email == false) {
        return true;
    } else {
        return false;   
    }

});

});

To add custom or field label or anything dynamic related to field being validated. you can pick anything through dom and add it anywhere with error message.

below is an example to add field label in start of required message instead of "this field".

jQuery.extend(jQuery.validator.messages, {

    required: function(result,e){

        let field_label = "This field ";

        if($(e).closest('.form-group').find('label').length > 0)
            field_label = $(e).closest('.form-group').find('label').html();

        return field_label+" is required.";

        },

});