isUndefined

isUndefined :: a → Boolean

Evaluates whether the given value is undefined

import isUndefined from 'deep-waters/isUndefined';

isUndefined(undefined); // → true
isUndefined(null); // → false
isUndefined(false); // → false

isUndefined, like any other type validator, is mostly used in composed validators:

import isString from 'deep-waters/isString';
import matchesPattern from 'deep-waters/matchesPattern';

const isEmail = compose(
  isString,
  matchesPattern(/^\w+([.-]?\w+)*@\w+([.-]?\w+)*(\.\w{2,3})+$/),
);

isUndefined is built on top of ofClass validator and rely on Object.prototype.toString to check on the received value type in order to avoid typeof weird behaviours and encouraging a runtime strict type validation.