Why is null an object and what's the difference between null and undefined?

Question

Why is null considered an object in JavaScript?

Is checking

if ( object == null )
      Do something

the

Answer 1

Use null to define something as having no value, use undefined when you expect something might not be defined at all.

For example, if a variable has no value, assign it as null.

var weDontHaveAValue = null;

If you expect that something might be not defined at all, e.g. an optional options argument, use undefined.

if (typeof args.optionalParam !== 'undefined') { }