TypeScript Language Specification Version 1.8 January, 2016 Microsoft is making this Specification available under the Open Web Foundation Final Specification Agreement Version 1.0 ("OWF 1.0") as of October 1, 2012. The OWF 1.0 is available at http://www.openwebfoundation.org/legal/the-owf-1-0-agreements/owfa-1-0. TypeScript is a trademark of Microsoft Corporation. Table of Contents 1 Introduction ................................................................................................................................................................................... 1 1.1 Ambient Declarations ..................................................................................................................................................... 3 1.2 Function Types .................................................................................................................................................................. 3 1.3 Object Types ...................................................................................................................................................................... 4 1.4 Structural Subtyping ....................................................................................................................................................... 6 1.5 Contextual Typing ............................................................................................................................................................ 7 1.6 Classes .................................................................................................................................................................................. 8 1.7 Enum Types ..................................................................................................................................................................... 10 1.8 Overloading on String Parameters......................................................................................................................... 12 1.9 Generic Types and Functions ................................................................................................................................... 12 1.10 Namespaces .................................................................................................................................................................... 14 1.11 Modules ............................................................................................................................................................................ 16 2 Basic Concepts .......................................................................................................................................................................... 17 2.1 Grammar Conventions ................................................................................................................................................ 17 2.2 Names ................................................................................................................................................................................ 17 2.2.1 Reserved Words ........................................................................................................................................................ 18 2.2.2 Property Names ........................................................................................................................................................ 18 2.2.3 Computed Property Names ................................................................................................................................. 19 2.3 Declarations ..................................................................................................................................................................... 19 2.4 Scopes ............................................................................................................................................................................... 22 3 Types ............................................................................................................................................................................................. 25 3.1 The Any Type .................................................................................................................................................................. 26 3.2 Primitive Types ............................................................................................................................................................... 26 3.2.1 The Number Type .................................................................................................................................................... 26 3.2.2 The Boolean Type .................................................................................................................................................... 27 3.2.3 The String Type ......................................................................................................................................................... 27 3.2.4 The Symbol Type ...................................................................................................................................................... 27 3.2.5 The Void Type............................................................................................................................................................ 28 3.2.6 The Null Type ............................................................................................................................................................. 28 3.2.7 The Undefined Type ................................................................................................................................................ 29 3.2.8 Enum Types ................................................................................................................................................................ 29 3.2.9 String Literal Types .................................................................................................................................................. 29 3.3 Object Types ................................................................................................................................................................... 29 3.3.1 Named Type References ....................................................................................................................................... 30 3.3.2 Array Types ................................................................................................................................................................. 30 3.3.3 Tuple Types ................................................................................................................................................................ 30 3.3.4 Function Types .......................................................................................................................................................... 31 3.3.5 Constructor Types .................................................................................................................................................... 31 i 3.3.6 Members ..................................................................................................................................................................... 31 3.4 Union Types..................................................................................................................................................................... 32 3.5 Intersection Types ......................................................................................................................................................... 34 3.6 Type Parameters ............................................................................................................................................................ 35 3.6.1 Type Parameter Lists ............................................................................................................................................... 35 3.6.2 Type Argument Lists ............................................................................................................................................... 36 3.6.3 This-types .................................................................................................................................................................... 37 3.7 Named Types .................................................................................................................................................................. 38 3.8 Specifying Types ............................................................................................................................................................ 39 3.8.1 Predefined Types ...................................................................................................................................................... 39 3.8.2 Type References ....................................................................................................................................................... 40 3.8.3 Object Type Literals ................................................................................................................................................. 41 3.8.4 Array Type Literals ................................................................................................................................................... 42 3.8.5 Tuple Type Literals