12         

Ambient declarations are used to provide static typing over existing JavaScript code. Ambient declarations differ from regular declarations in that no JavaScript code is emitted for them. Instead of introducing new variables, functions, classes, enums, or modules, ambient declarations provide type information for entities that exist “ambiently” and are included in a program by external means, for example by referencing a JavaScript library in a <script/> tag.

   

12.1    

         

AmbientDeclaration:
declare   AmbientVariableDeclaration
declare   AmbientFunctionDeclaration
declare   AmbientClassDeclaration
declare   AmbientEnumDeclaration
declare   AmbientModuleDeclaration
declare   

         

12.1.1     

   

AmbientVariableDeclaration:
var   Identifier    TypeAnnotation_opt   ;

   

   

12.1.2     

   

AmbientFunctionDeclaration:
function   ;

         

   

12.1.3     

   

AmbientClassDeclaration:
class   Identifier   TypeParameters_opt   ClassHeritage   {   }

AmbientClassBody:
AmbientClassBodyElements_opt

AmbientClassBodyElements:
AmbientClassBodyElement
AmbientClassBodyElements   AmbientClassBodyElement

AmbientClassBodyElement:
AmbientConstructorDeclaration
AmbientMemberDeclaration
IndexSignature

AmbientConstructorDeclaration:
constructor   (   ParameterList_opt   )   ;

AmbientMemberDeclaration:
PublicOrPrivate_opt   static_opt   PropertyName   TypeAnnotation_opt   ;
PublicOrPrivate_opt   static_opt   PropertyName   CallSignature   ;

12.1.4  Ambient Enum Declarations

An ambient enum declaration declares an enum type and an enum object in the containing module.

AmbientEnumDeclaration:
enum   Identifier   {   AmbientEnumBody_opt   }

AmbientEnumBody:
AmbientEnumMemberList   ,_opt

AmbientEnumMemberList:
AmbientEnumMember
AmbientEnumMemberList   ,   AmbientEnumMember

AmbientEnumMember:
PropertyName
PropertyName   =   IntegerLiteral

An AmbientEnumMember that includes an IntegerLiteral value is considered a constant member. An AmbientEnumMember with no IntegerLiteral value is considered a computed member.

12.1.5  Ambient Module Declarations

An ambient module declaration declares an internal module.

AmbientModuleDeclaration:
module   IdentifierPath   {   AmbientModuleBody   }

AmbientModuleBody:
AmbientModuleElements_opt

AmbientModuleElements:
AmbientModuleElement
AmbientModuleElements   AmbientModuleElement

AmbientModuleElement:
export_opt   AmbientVariableDeclaration
export_opt   AmbientFunctionDeclaration
export_opt   AmbientClassDeclaration
export_opt   InterfaceDeclaration
export_opt   AmbientEnumDeclaration
export_opt   AmbientModuleDeclaration
export_opt   ImportDeclaration

Except for ImportDeclarations, AmbientModuleElements always declare exported entities regardless of whether they include the optional export modifier.

12.1.6  Ambient External Module Declarations

An AmbientExternalModuleDeclaration declares an external module. This type of declaration is permitted only in the global module. The StringLiteral must specify a top-level external module name. Relative external module names are not permitted.

AmbientExternalModuleDeclaration:
module   StringLiteral   {    AmbientExternalModuleBody   }

AmbientExternalModuleBody:
AmbientExternalModuleElements_opt

AmbientExternalModuleElements:
AmbientExternalModuleElement
AmbientExternalModuleElements   AmbientExternalModuleElement

AmbientExternalModuleElement:
AmbientModuleElement
ExportAssignment
export_opt   ExternalImportDeclaration

An ExternalImportDeclaration in an AmbientExternalModuleDeclaration may reference other external modules only through top-level external module names. Relative external module names are not permitted.

If an ambient external module declaration includes an export assignment, it is an error for any of the declarations with the module to specify an export modifier. If an ambient external module declaration contains no export assignment, entities declared in the module are exported regardless of whether their declarations include the optional export modifier.