Yup validation - one field required but not both at the same time

3/5/2020
#yup, #validation, #javascript, #form

Recently I was working with yup for form validation and I faced the following problem:

I have two fields inside my form. I want the user to provide one of them but not both at the same time. I’ve played a little bit with different ideas to get solution below. It is using test and when functions from yup:

import { object, string } from 'yup';

const schema = object().shape(
  {
    userName: string()
      .test(
        'notBothAtTheSameTime', // test name
        'You cannot pass user name at the same time as user email', // validation message to the user
        // it has to be function definition to use `this`
        function(userName) {
          const { userEmail } = this.parent;
          if (userEmail && userName) {
            return false; // when user enters both userEmail & userName do not validate form
          }
          return true;
        }
      )
      .when(['userEmail'], {
        is: userEmail => !userEmail,
        then: string().required('User name is required'),
      }),
    userEmail: string()
      .test(
        'notBothAtTheSameTime',
        'You cannot pass user email at the same time as user name',
        function(userEmail) {
          const { userName } = this.parent;
          if (userName && userEmail) {
            return false;
          }
          return true;
        }
      )
      .when(['userName'], {
        is: userName => !userName,
        then: string().required('User email is required'),
     email
  [['userName', 'userEmail']] // important to add
);

If you want you can extract it to its own function via addMethod. That’s all 🎉. Now user should get and error when they provide both userName & userEmail.

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