5.10 Equality Checks

Use identity operators (===/!==) except in the cases documented below.

5.10.1 Exceptions Where Coercion is Desirable

Catching both null and undefined values:

if (someObjectOrPrimitive == null) {
  // Checking for null catches both null and undefined for objects and
  // primitives, but does not catch other falsy values like 0 or the empty
  // string.
}