isNaN() (is Not a Number): isUndefined, isNotSet, isNotDefined, void, ['item'], {prop:'item'}, {} !isNaN() (is a number): null, number, [], "", 0, false isNull typeof object isNull === null isNull == null isNull == undefined isNull is a number (!isNaN) isUndefined typeof undefined isUndefined == null isUndefined === undefined isUndefined == undefined isUndefined isNaN isNotSet typeof undefined isNotSet == null isNotSet === undefined isNotSet == undefined isNotSet isNaN isNotDefined typeof undefined isNotDefined == null isNotDefined === undefined isNotDefined == undefined isNotDefined isNaN isVoid typeof undefined isVoid == null isVoid === undefined isVoid == undefined isVoid isNaN isArray typeof object isArray instanceof Array isArray instanceof Object isArray isNaN isObject typeof object isObject instanceof Object isObject isNaN isEmptyArray typeof object isEmptyArray instanceof Array isEmptyArray instanceof Object isEmptyArray == false isEmptyArray == 0 isEmptyArray == "" isEmptyArray is a number (!isNaN) isEmptyObject typeof object isEmptyObject instanceof Object isEmptyObject isNaN isEmptyString typeof string isEmptyString == false isEmptyString == 0 isEmptyString == [] isEmptyString === "" isEmptyString == "" isEmptyString is a number (!isNaN) isZero typeof number isZero == false isZero === 0 isZero == 0 isZero == [] isZero == "" isZero is a number (!isNaN) isFalse typeof boolean isFalse === false isFalse == false isFalse == 0 isFalse == [] isFalse == "" isFalse is a number (!isNaN)