express-yup-middleware

express-yup-middleware is an express middleware that uses Yup schemas to validate a request and return a response with errors.

Basic schema validation

import { expressYupMiddleware } from 'express-yup-middleware'

import * as Yup from 'yup'

const schemaValidator = {
  schema: {
    query: {
      yupSchema: Yup.object().shape({
        testQueryParam: Yup.string().required('requiredTestQueryParam'),
      }),
    },
    body: {
      yupSchema: Yup.object().shape({
        testBodyProperty: Yup.string().required('requiredTestBodyProperty'),
      }),
    },
    params: {
      yupSchema: Yup.object().shape({
        testParams: Yup.string().required('requiredTestParams'),
      }),
    },
  },
}

app.post('/test', expressYupMiddleware({ schemaValidator }))

{
  "errors": {
    "params": [
      {
        "message": "requiredTestParams",
        "propertyPath": "testParams"
      }
    ],
    "body": [
      {
        "message": "requiredTestBodyProperty",
        "propertyPath": "testBodyProperty"
      }
    ],
    "query": [
      {
        "message": "requiredTestQueryParam",
        "propertyPath": "testQueryParam"
      }
    ]
  }
}

Setting custom error messages

Make sure the key in the Yup schema (requiredTestBodyProperty) matches the property name in the error messages object.

const schemaValidator = {
  schema: {
    body: {
      yupSchema: Yup.object().shape({
        testBodyProperty: Yup.string().required('requiredTestBodyProperty'),
      }),
    },
  },
  errorMessages: {
    requiredTestBodyProperty: {
      key: 'tes-body-property-required',
      message: 'The "testBodyProperty" property is required!',
    },
  },
}

{
  "errors": {
    "body": [
      {
        "key": "tes-body-property-required",
        "message": "The \"testBodyProperty\" property is required!",
        "propertyPath": "testBodyProperty"
      }
    ]
  }
}

Cross-validation using any properties from your payload

You can cross-validate properties of your payload using a custom Yup test and accessing them by calling this.options.context.

const schemaValidator = {
  schema: {
    body: {
      yupSchema: Yup.object().shape({
        numberToValidate: Yup.string().test({
          message: 'Check if your number corresponds with the given type',
          test(this: Yup.TestContext, numberToValidate: any) {
            const mod = numberToValidate % 2
            // As you can see in the next line, the req is passed to the context
            const type = this.options.context['payload'].params.type

            if (!type) {
              return false
            }

            if (type === 'even') {
              return mod === 0
            }

            if (type === 'odd') {
              return mod !== 0
            }

            return false
          },
        }),
      }),
    },
  },
}

app.post('/test/:type', expressYupMiddleware({ schemaValidator }))

Validating a custom property in the request

The middleware default properties checked in the req (Express request) are body, params and query. If you want to validate anything else, you need to use the following option.

const schemaValidator = {
  schema: {
    headers: {
      yupSchema: Yup.object().shape({
        testHeaderProperty: Yup.string().required('requiredHeaderProperty'),
      }),
    },
  },
}

app.post('/test', expressYupMiddleware({ schemaValidator, propertiesToValidate: ['headers'] }))

{
  "errors": {
    "headers": [
      {
        "message": "requiredHeaderProperty",
        "propertyPath": "testHeaderProperty"
      }
    ]
  }
}

Using a custom error status code

Adding the expectedStatusCode option, your will receive the given status code if anything fails during the validation.

app.post('/test', expressYupMiddleware({ schemaValidator, expectedStatusCode: 418 }))