Type Hierarchy

Types in Flow form a hierarchy based on subtyping:

Click on a node to go to the documentation for that type.

Types appearing higher in this graph are more general, while those appearing lower are more specific. An arrow pointing from type A to type B means that A is a subtype of B. For example, the type string is a subtype of ?string.

How can any be at both the top and the bottom? Because it is unsafe. This is denoted with a dotted line.

See Also​

• Subtypes — the theory behind how types relate in the hierarchy
• Any — the unsafe type that is both top and bottom
• Unknown — the safe top type (supertype of all types)
• Empty — the bottom type (subtype of all types)
• Variance — how covariance and contravariance affect subtype relationships