TypeScript Language Specification v1.5

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......................................................................................................................... 11
1.9 Generic Types and Functions ................................................................................................................................... 12
1.10 Modules ............................................................................................................................................................................ 14
2 Basic Concepts .......................................................................................................................................................................... 17
2.1 Grammar Conventions ................................................................................................................................................ 17
2.2 Namespaces and Named Types .............................................................................................................................. 17
2.3 Declarations ..................................................................................................................................................................... 18
2.4 Scopes ............................................................................................................................................................................... 20
3 Types ............................................................................................................................................................................................. 23
3.1 The Any Type .................................................................................................................................................................. 24
3.2 Primitive Types ............................................................................................................................................................... 24
3.2.1 The Number Type .................................................................................................................................................... 24
3.2.2 The Boolean Type .................................................................................................................................................... 25
3.2.3 The String Type ......................................................................................................................................................... 25
3.2.4 The Void Type............................................................................................................................................................ 25
3.2.5 The Null Type ............................................................................................................................................................. 26
3.2.6 The Undefined Type ................................................................................................................................................ 26
3.2.7 Enum Types ................................................................................................................................................................ 26
3.2.8 String Literal Types .................................................................................................................................................. 27
3.3 Object Types ................................................................................................................................................................... 27
3.3.1 Named Type References ....................................................................................................................................... 27
3.3.2 Array Types ................................................................................................................................................................. 27
3.3.3 Tuple Types ................................................................................................................................................................ 28
3.3.4 Function Types .......................................................................................................................................................... 29
3.3.5 Constructor Types .................................................................................................................................................... 29
3.3.6 Members ..................................................................................................................................................................... 29
3.4 Union Types..................................................................................................................................................................... 30
3.4.1 Contextual Union Types ........................................................................................................................................ 31
3.5 Type Parameters ............................................................................................................................................................ 32
3.5.1 Type Parameter Lists ............................................................................................................................................... 32
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