redux-form/redux-form

// @flow
import plain from './structure/plain'
import type { Structure } from './types'

export type Validator = { (values: any, props: Object): Object }

const toArray = value => (Array.isArray(value) ? value : [value])

const getError = (value: any, values: Object, props: Object, validators: any, name: string) => {
  const array = toArray(validators)
  for (let i = 0; i < array.length; i++) {
    const error = array[i](value, values, props, name)
    if (error) {
      return error
    }
  }
}

export default function generateValidator(
  validators: Object,
  { getIn }: Structure<any, any>
): Validator {
  return (values: any, props: Object) => {
    let errors = {}
    Object.keys(validators).forEach(name => {
      const value = getIn(values, name)
      const error = getError(value, values, props, validators[name], name)
      if (error) {
        errors = plain.setIn(errors, name, error)
      }
    })
    return errors
  }
}