no-null-undefined-union.md

Pattern: Union type with null and undefined

Issue: -

Description

Disallows explicitly declared or implicitly returned union types with both null and undefined as members.

Rationale: A union type that includes both null and undefined is either redundant or fragile. Enforcing the choice between the two allows the triple-equals rule to exist without exceptions, and is essentially a more flexible version of the no-null-keyword rule. Optional parameters are not considered to have the type undefined.

Further Reading

• TSLint - no-null-undefined-union