TypeScript Language Specification v1.5

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IndexSignature: [ Identifier : string ] TypeAnnotation [ Identifier : number ] TypeAnnotation There are two kinds of index signatures: String index signatures, specified using index type string, define type constraints for all properties and numeric index signatures in the containing type. Specifically, in a type with a string index signature of type T, all properties and numeric index signatures must have types that are assignable to T. Numeric index signatures, specified using index type number, define type constraints for all numerically named properties in the containing type. Specifically, in a type with a numeric index signature of type T, all numerically named properties must have types that are assignable to T. A numerically named property is a property whose name is a valid numeric literal. Specifically, a property with a name N for which ToNumber(N) is not NaN, where ToNumber is the abstract operation defined in ECMAScript specification. An object type can contain at most one string index signature and one numeric index signature. Index signatures affect the determination of the type that results from applying a bracket notation property access to an instance of the containing type, as described in section 4.10. 3.8.5 Method Signatures A method signature is shorthand for declaring a property of a function type. MethodSignature: PropertyName ? opt CallSignature If the identifier is followed by a question mark, the property is optional. Otherwise, the property is required. Only object type literals and interfaces can declare optional properties. A method signature of the form f < T1, T2, ... > ( p1, p2, ... ) : R is equivalent to the property declaration f : { < T1, T2, ... > ( p1, p2, ... ) : R } A literal type may overload a method by declaring multiple method signatures with the same name but differing parameter lists. Overloads must either all be required (question mark omitted) or all be optional (question mark included). A set of overloaded method signatures correspond to a declaration of a single property with a type composed from an equivalent set of call signatures. Specifically 46
f < T1, T2, ... > ( p1, p2, ... ) : R ; f < U1, U2, ... > ( q1, q2, ... ) : S ; ... is equivalent to f : { < T1, T2, ... > ( p1, p2, ... ) : R ; < U1, U2, ... > ( q1, q2, ... ) : S ; ... } ; In the following example of an object type { } func1(x: number): number; func2: (x: number) => number; func3: { (x: number): number }; // Method signature // Function type literal // Object type literal the properties 'func1', 'func2', and 'func3' are all of the same type, namely an object type with a single call signature taking a number and returning a number. Likewise, in the object type { } func4(x: number): number; func4(s: string): string; func5: { (x: number): number; (s: string): string; }; the properties 'func4' and 'func5' are of the same type, namely an object type with two call signatures taking and returning number and string respectively. 3.9 Type Aliases A type alias declaration introduces a type alias in the containing module. TypeAliasDeclaration: type Identifier = Type ; A type alias serves as an alias for the type specified in the type alias declaration. Unlike an interface declaration, which always introduces a named object type, a type alias declaration can introduce a name for any kind of type, including primitive types and union types. 47
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TypeScript Language Specification V
Page 3 and 4: Table of Contents 1 Introduction ..
Page 5 and 6: 4.9.1 Standard Function Expressions
Page 7 and 8: 9.1 Enum Declarations .............
Page 9 and 10: 1 Introduction JavaScript applicati
Page 11 and 12: 1.1 Ambient Declarations An ambient
Page 13 and 14: call '$' as a function. The behavio
Page 15 and 16: function getX(p: Point) { return p.
Page 17 and 18: This TypeScript class declaration c
Page 19 and 20: Section 9 describes how programmers
Page 21 and 22: Interface definitions, like the one
Page 23 and 24: TypeScript modules provide a mechan
Page 25 and 26: 2 Basic Concepts The remainder of t
Page 27 and 28: Each enum declaration has a declara
Page 29: When an identifier is resolved as a
Page 32 and 33: which infers the type of 'x' to be
Page 34 and 35: The only possible values for the Vo
Page 36 and 37: interface Array { length: number; [
Page 38 and 39: 3.4 Union Types Union types represe
Page 40 and 41: 3.5 Type Parameters A type paramete
Page 42 and 43: 3.6 Named Types Classes, interfaces
Page 44 and 45: 3.7.1 Predefined Types The any, num
Page 46 and 47: TypeMember: PropertySignature CallS
Page 48 and 49: 3.7.8 Constructor Type Literals A c
Page 50 and 51: 3.8.2 Call Signatures A call signat
Page 52 and 53: RestParameter: ... Identifier TypeA
Page 56 and 57: Type aliases are referenced using t
Page 58 and 59: o o If each type in U has an appare
Page 60 and 61: o o o M is a non-specialized call o
Page 62 and 63: 3.10.5 Contextual Signature Instant
Page 64 and 65: interface List { data: T; next: Lis
Page 66 and 67: 4.3 Identifiers When an expression
Page 68 and 69: of the object literal includes a nu
Page 70 and 71: A super call invokes the constructo
Page 72 and 73: ( id ) => { ... } ( id ) => expr Th
Page 74 and 75: A dot notation property access of t
Page 76 and 77: If func is of type Any, or of an ob
Page 78 and 79: An example: signature are fixed, an
Page 80 and 81: This rule means that the call to 'f
Page 82 and 83: 4.14.4 The delete Operator The 'del
Page 84 and 85: Any Boolean Number String Other Any
Page 86 and 87: where ??= is one of the compound as
Page 88 and 89: 4.18 The Comma Operator The comma o
Page 90 and 91: function foo(x: number | string) {
Page 92 and 93: function processValue(value: number
Page 95 and 96: 5 Statements This chapter describes
Page 97 and 98: BindingProperty: Identifier Initial
Page 99 and 100: Similarly, an array destructuring d
Page 101 and 102: 5.5 Continue Statements A 'continue
Page 103 and 104: 6 Functions TypeScript extends Java
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function f(x: number) { if (x
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When the output target is ECMAScrip
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101
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An interface has the members specif
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interface Document { createElement(
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8 Classes TypeScript supports class
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The following constraints must be s
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Private and protected accessibility
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interface A { x: number; f: () => v
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ConstructorOverloads: ConstructorOv
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BaseClass.apply(this, arguments); a
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Initializer expressions for instanc
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var x = A.create(); // new A() var
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MemberVariableAssignments is a sequ
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In addition, the '__extends' functi
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9 Enums An enum type is a distinct
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An identifier or property access th
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var Color; (function (Color) { Colo
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If the declaration of 'M' above had
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module A { export interface X { s:
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module outer { var local = 1; expor
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where ModuleName is the name of the
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DeclarationElement: ExportAssignmen
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that source file is considered an e
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Unlike a non-instantiated internal
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import g = require("./geometry"); v
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12.1.3 Ambient Class Declarations A
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An ExternalImportDeclaration in an
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PrimaryType: ParenthesizedType Pred
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ParameterList: RequiredParameterLis
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UnaryExpression: ( Modified ) … <
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ClassExtendsClause: extends ClassTy
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ModuleBody: ModuleElements opt Modu
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AmbientClassBodyElements: AmbientCl
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TypeScript Language Specification v1.5

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