Union types

The structural union type, written (t1,t2,tN), consists of two or more member types, containing all possible values of the member types.

(decimal,string)

Restrictions

• Unions contain two or more members.

Default value

The default value of an union type is determined as follows:

1. If it contains void, then undefined.
2. If it contains null, then null.
3. No default value.

Nullability

The following shorthands are available for nullability:

• “t?” is equivalent to (t,null).
• “t!” removes null and/or void from t.