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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.