TypeScript Language Specification v1.5

var c = Color.Red;
console.log(Color[c]); // Outputs "Red"
9.2 Enum Members
The body of an enum declaration defines zero or more enum members which are the named values of the
enum type. Each enum member has an associated numeric value of the primitive type introduced by the
enum declaration.
EnumBody:
EnumMemberList , opt
EnumMemberList:
EnumMember
EnumMemberList , EnumMember
EnumMember:
PropertyName
PropertyName = EnumValue
EnumValue:
AssignmentExpression
Enum members are either constant members or computed members. Constant members have known
constant values that are substituted in place of references to the members in the generated JavaScript
code. Computed members have values that are computed at run-time and not known at compile-time.
No substitution is performed for references to computed members.
An enum member is classified as follows:
If the member declaration specifies no value, the member is considered a constant enum
member. If the member is the first member in the enum declaration, it is assigned the value zero.
Otherwise, it is assigned the value of the immediately preceding member plus one, and an error
occurs if the immediately preceding member is not a constant enum member.
If the member declaration specifies a value that can be classified as a constant enum expression
(as defined below), the member is considered a constant enum member.
Otherwise, the member is considered a computed enum member.
Enum value expressions must be of type Any, the Number primitive type, or the enum type itself.
A constant enum expression is a subset of the expression grammar that can be evaluated fully at
compile time. An expression is considered a constant enum expression if it is one of the following:
A numeric literal.
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