isNaN_.isNaN(object) Returns true if object is NaN. Note: this is not the same as the native isNaN

isUndefined_.isUndefined(value) Returns true if value is undefined.

isNumber_.isNumber(object) Returns true if object is a Number (including NaN).

isBoolean_.isBoolean(object) Returns true if object is either true or false.

has_.has(object, key) Does the object contain the given key? Identical to object.hasOwnProperty(key), but uses a safe reference

invert_.invert(object) Returns a copy of the object where the keys have become the values and the values the keys. For this

isArray_.isArray(object) Returns true if object is an Array.

isError_.isError(object) Returns true if object inherits from an Error.