Validating file size and format with YUP

Question

I have a form using reactjs + formik + yup. I have a multi file upload field. I want to validate the file format and max size using yup. How can I do this?

Answer 1

Expanding on Devin's answer, you can implement that validation with yup.

    const schema = Yup.object().shape({
       files: Yup.array()
         .nullable()
         .required('VALIDATION_FIELD_REQUIRED')
         .test('is-correct-file', 'VALIDATION_FIELD_FILE_BIG', checkIfFilesAreTooBig)
         .test(
           'is-big-file',
           'VALIDATION_FIELD_FILE_WRONG_TYPE',
           checkIfFilesAreCorrectType
         ),
})

Where the validation functions are:

export function checkIfFilesAreTooBig(files?: [File]): boolean {
  let valid = true
  if (files) {
    files.map(file => {
      const size = file.size / 1024 / 1024
      if (size > 10) {
        valid = false
      }
    })
  }
  return valid
}

export function checkIfFilesAreCorrectType(files?: [File]): boolean {
  let valid = true
  if (files) {
    files.map(file => {
      if (!['application/pdf', 'image/jpeg', 'image/png'].includes(file.type)) {
        valid = false
      }
    })
  }
  return valid
}