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Yup is a JavaScript schema validation library that allows developers to validate data structures and ensure that they meet certain requirements. One of the most powerful features of Yup is its ability to conditionally validate array fields. This means that you can set up rules for validating arrays based on specific conditions, such as the length of the array or the values contained within it.

In this guide, we will walk you through the process of conditionally validating array fields with Yup. We will cover the basics of Yup validation, how to set up conditional validation rules, and some common use cases for this feature.

Getting Started with Yup Validation

Before we dive into conditional validation, let’s review the basics of Yup validation. Yup allows you to define a schema for your data structure, which includes the types of each field and any validation rules that should be applied. Here’s an example schema for a simple user object:

“`javascript

const userSchema = yup.object().shape({

name: yup.string().required(),

email: yup.string().email().required(),

age: yup.number().positive().integer().required(),

});

“`

In this schema, we have defined three fields for our user object: name, email, and age. Each field has a type (string or number) and a set of validation rules. For example, the name field is required, meaning that it must be present in the object, and it must be a string.

To validate an object against this schema, we can use the validate method:

“`javascript

const user = {

name: ‘John Doe’,

email: ‘john.doe@example.com’,

age: 30,

};

userSchema.validate(user)

.then(validUser => console.log(validUser))

.catch(error => console.log(error));

“`

In this example, we are validating a user object against our schema. If the object meets all of the validation rules, the validate method will return the object. If there are any validation errors, it will throw an error.

Now that we have reviewed the basics of Yup validation, let’s move on to conditional validation.

Setting Up Conditional Validation Rules

Conditional validation in Yup allows you to set up rules that only apply under certain conditions. For example, you might want to require a certain field only if another field has a specific value, or you might want to validate an array only if it contains a certain number of items.

To set up conditional validation rules in Yup, you can use the when method. The when method takes two arguments: a field name and a configuration object. The configuration object specifies the condition under which the validation rule should apply.

Here’s an example of how to use the when method to conditionally validate an array field:

“`javascript

const userSchema = yup.object().shape({

name: yup.string().required(),

email: yup.string().email().required(),

age: yup.number().positive().integer().required(),

hobbies: yup.array().when(‘age’, {

is: age => age >= 18,

then: yup.array().min(1).required(),

otherwise: yup.array(),

}),

});

“`

In this schema, we have added a hobbies field to our user object. We want to require at least one hobby if the user is 18 or older, but we don’t want to require any hobbies if the user is younger than 18.

To set up this conditional validation rule, we use the when method on the hobbies field. We pass in the name of the age field as the first argument, and a configuration object as the second argument. The configuration object has two properties: is and then.

The is property is a function that takes the value of the age field and returns a boolean. In this case, we are checking if the age is greater than or equal to 18.

The then property is a Yup schema that will be applied if the condition is true. In this case, we are requiring the hobbies field to have a minimum length of 1.

The otherwise property is a Yup schema that will be applied if the condition is false. In this case, we are allowing the hobbies field to be an empty array.

Common Use Cases for Conditional Validation

Conditional validation can be used in a variety of situations to ensure that your data meets specific requirements. Here are some common use cases for this feature:

– Requiring certain fields only if other fields have specific values. For example, you might want to require a phone number only if the user has selected a specific country.

– Validating arrays based on their length or contents. For example, you might want to require a minimum number of items in an array, or you might want to ensure that all items in an array are unique.

– Validating nested objects based on their properties. For example, you might want to require a certain property in a nested object only if another property has a specific value.

Conclusion

Yup’s conditional validation feature allows

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• Source: https://zephyrnet.com/yup-validate-array-fields-conditionally-codementor/