Enum type

Enum types are used to define a set of named integer constants. All enum members must be explicitly assigned integer literals. They cannot be assigned string literals. Enum members are not implicitly initialized with auto-incremented values. Their values must be explicitly given.

enum Color { Red = -1, Green = 0, Blue = 1 }

Enum declarations must be at top-level. They may not be contained in a function body.

An enum type is intended to be a subtype of integer. But a variable of enum type may hold an arbitrary integer value. For example,

const i = 2
let c: Color = i    // type error

This causes a static type error since i is statically typed as integer but the type of c is Color. Integer type is not a subtype of Color. However,

let k: Color = (i as any)    // OK

When a variable of any type holds an integer value, the value may be assigned to a variable of enum type. Currently, no runtime type checking is performed.