But then you have the problem that typeof null === 'object'.
This is especially useful if you are using TypeScript (or Flow I assume) because the type checker can give you an error at compile time. After performing the runtime check, TypeScript will know that null/undefined is not possible.
See this example https://goo.gl/AyoC3T
`const isString = myVar => typeof myVar !== 'string'`
This is more reusable and more idiomatic in my opinion than null/undefined checks