Validate Field in Yup based on multiple related field values with Yup.ref and .test

I’ve created a multi-step form in “react”: “^17.0.1”, “yup”: “^0.29.3”, and “formik”: “^2.2.3”.

I want to check that when a user enters in a their Birth Day (dobD) that it is valid based on Birth Month (dobM) and Birth Year (dobY).

I have 3 separate inputs. dobM, dobD, dobY

The first check for dobD works (i.e the user can only enter a value between 1 and 31) however it doesn’t validate correctly if it a month with less than 31 days (for example June or September) OR if the month is February (which only 28 days except for leap years).

I tried using Yup.ref to reference the year and month fields inside of the day field validation, however if I type for the month 04, the user can still enter 31 which is incorrect (since April (04) only has 30 days).

Any ideas how can I fix this? Thank you!

Here is the validation in Yup I’m currently using:

  // Step 3: Date of Birth
  Yup.object().shape({
    dobM: Yup.string()
      .test(
        'dobM',
        'Invalid Month',
        value => {
          if (value < 1 || value > 12) {
            return false;
          }
          return true;
        }
      )
      .min(2, 'Invalid')
      .max(2, 'Invalid')
      .required('Required'),
    dobY: Yup.string()
      .test(
        'dobY',
        'Valid Year required',
        value => {
          const today = new Date();
          const adultYear = today.getFullYear() - 17;
          if (value < 1900 || value > adultYear) {
            return false;
          }
          return true;
        }
      )
      .min(4, 'Must be 4 digits')
      .max(4, 'Must be 4 digits')
      .required('Valid Year required'),
    dobD: Yup.string()
      .test(
        'dobD',
        'Invalid Day',
        value => {
          if (value < 1 || value > 31) {
            return false;
          }

          // Check months with less than 31 days - DOESNT WORK
          // 4. April
          // 6. June
          // 9. September
          // 11. November
          if ((Yup.ref('dobM') == 4 || Yup.ref('dobM') == 6 || Yup.ref('dobM') == 9 || Yup.ref('dobM') == 11) && value == 31) {
            return false;
          }

          // If February - DOESNT WORK
             if (Yup.ref('dobM') == 2) {
             const isLeapYear = Yup.ref('dobY') % 4 == 0 && (Yup.ref('dobY') % 100 != 0 || Yup.ref('dobY') % 400 == 0);

             if (day > 29 || (day == 29 && !isLeapYear)) {
               return false;
             }
           }

          return true;
        }
      )
      .min(2, 'Invalid')
      .max(2, 'Invalid')
      .required('Required'),  
  }), 

Answer

Posting my solution in hopes that this helps someone else.

I was using Yup.ref incorrectly (Yup.ref(‘fieldname’) is an object, not a single value).

** To be able to access another field in Yup I converted from an arrow function to a regular function in my test, and then could access the field values using

this.options.parent.FIELD_NAME

seen in this example:

function(day) {
          const month = this.options.parent.dobM;
          const year = this.options.parent.dobY;
 
         // check whatever you want with the value of month and year
}

Full DOB validation:

  // Step 3: Date of Birth
  Yup.object().shape({
    dobM: Yup.string()
      .matches(/^(0[1-9]|1[012])$/, 'Invalid Month')
      .test(
        'dobM',
        'Invalid Month',
        value => {
          if (value < 1 || value > 12) {
            return false;
          }
          return true;
        }
      )
      .min(2, 'Invalid')
      .max(2, 'Invalid')
      .required('Required'),
    dobY: Yup.string()
      .test(
        'dobY',
        'Valid Year required',
        value => {
          const today = new Date();
          const adultYear = today.getFullYear() - 17;
          if (value < 1900 || value > adultYear) {
            return false;
          }
          return true;
        }
      )
      .matches(/^[0-9]+$/, 'Must be only digits')
      .min(4, 'Must be 4 digits')
      .max(4, 'Must be 4 digits')
      .required('Valid Year required'),
    dobD: Yup.string()
      .test(
        'dobD',
        'Invalid Day',
        function(day) {
          const month = this.options.parent.dobM;
          const year = this.options.parent.dobY;
          // February
          if (month == 2) {
            const isLeapYear = year % 4 == 0 && (year % 100 != 0 || year % 400 == 0);

            if (day > 29 || (day == 29 && !isLeapYear)) {
              return false;
            }
          }
          return true;
        }
      )
      .test(
        'dobD',
        'Invalid Day',
        function(day) {
          const month = this.options.parent.dobM;
          // Check months with less than 31 days
          // 4. April
          // 6. June
          // 9. September
          // 11. November
          if ((month == 4 || month == 6 || month == 9 || month == 11) && day == 31) {
            return false;
          }
          return true;
        }
      )
      .test(
        'dobD',
        'Invalid Day',
        day => {
          if (day < 1 || day > 31) {
            return false;
          }
          return true;
        }
      )
      .matches(/^[0-9]+$/, 'Digits Only')
      .min(2, 'Invalid Day')
      .max(2, 'Invalid Day')
      .required('Required'),  
  }),

Sidenote: For readability, I moved each check for dobD into it’s own Yup .test(), however it’s not required.