Joi Validations: Capture the value passed in Custom Error Message

Question

I am using Joi Library with NodeJs/Typescript for validations. Validating a request body for a Post Operation.

I am using the language option to provide custom messages for respective field validations.

Below is the code

const bodySchema = Joi.object().keys({
    // had to change from string to any so as to avoid multiple messages when empty
    field1: Joi.any().required().valid('Dummy').options({
        language: {
            any: {
                // wrt empty: specific error  message not displaying  with any but empty error is handled by allowOnly custom message. Anways there is no custom message for empty in requirements
                // empty: '!!The parameter \'field1\' cannot be empty. It must be \'Dummy\'',
                required: '!!The parameter \'field1\' is mandatory and must be the value \'Dummy\'',
                allowOnly: '!!Invalid value for parameter \'field1\'. It must be \'Dummy\''
            // how to capture value passed for field1 in the message?
            }
        }
    }),

How to Capture the wrong field value passed as requestBody in the custom error message

For eg if I pass request body for the POST endpoint

 {
  "field1": "wrongvalue",
 }    

Expected custom message Invalid value 'wrongvalue' for parameter \\'field1\\'. It must be \\'Dummy\\''

I have gone through JOI API but could not find any reference to doing this. While regex option has the facility to capture the value passed. {{value}} works in regex but not in other options.

Please let me know if there is a way to capture the value.

Answer 1

try this ......

const typeSchema = Joi.object({field1: Joi
    any()
    .required()
    .valid('Dummy')            
    .error(errors => {
      errors.forEach(err => {
        switch (err.type) {
          case "string.base":
          case "required":
            err.message = "field 1 is mandatory and must be the value";
            break;
          case "any.allowOnly":
            err.message = "field1 must be Dummy";
            break; 
          default:
            console.log('validate error type missing', err.type);
            break;
        }
      });
      return errors;
    }),

})