TypeScript Language Specification

2 Basic Concepts
The remainder of this document is the formal specification of the TypeScript programming language and
is intended to be read as an adjunct to the ECMAScript Language Specification (specifically, the ECMA-
262 Standard, 5 th Edition). This document describes the syntactic grammar added by TypeScript along
with the compile-time processing and type checking performed by the TypeScript compiler, but it only
minimally discusses the run-time behavior of programs since that is covered by the ECMAScript
specification.
2.1 Grammar Conventions
The syntactic grammar added by TypeScript language is specified throughout this document using the
existing conventions and production names of the ECMAScript grammar. In places where TypeScript
augments an existing grammar production it is so noted. For example:
CallExpression: ( Modified )
…
super Arguments
super . Identifier
The ‘( Modified )’ annotation indicates that an existing grammar production is being replaced, and the ‘…’
references the contents of the original grammar production.
2.2 Declarations
Declarations introduce names in the declaration spaces to which they belong. It is an error to have two
names with same spelling in the same declaration space. Declaration spaces exist as follows:
� The global module has a declaration space for global members (variables, functions, modules, and
constructor functions), and a declaration space for global types (modules, classes, and interfaces).
� Each module body has a declaration space for local members (variables, functions, modules, and
constructor functions), and a declaration space for local types (modules, classes, and interfaces).
Every declaration (whether local or exported) in a module contributes to one or both of these
declaration spaces.
� Each internal or external module has a declaration space for exported members and a declaration
space for exported types. All export declarations in the module contribute to these declaration
spaces. Each internal module’s export declaration spaces are shared with other internal modules
that have the same root module and the same qualified name starting from that root module.
� Each interface type has a declaration space for its members. An interface’s declaration space is
shared with other interfaces that have the same root module and the same qualified name
starting from that root module.
� Each object type literal has a declaration space for its members.
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