TypeScript Language Specification v1.5

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interface Point { x: number; y: number; length(): number; } The 'Point' member is a constructor function whose type corresponds to the declaration var Point: { new(x: number, y: number): Point; origin: Point; }; The context in which a class is referenced distinguishes between the class instance type and the constructor function. For example, in the assignment statement var p: Point = new Point(10, 20); the identifier 'Point' in the type annotation refers to the class instance type, whereas the identifier 'Point' in the new expression refers to the constructor function object. 8.1.1 Class Heritage <strong>Specification</strong> The heritage specification of a class consists of optional extends and implements clauses. The extends clause specifies the base class of the class and the implements clause specifies a set of interfaces for which to validate the class provides an implementation. ClassHeritage: ClassExtendsClause opt ImplementsClause opt ClassExtendsClause: extends ClassType ClassType: TypeReference ImplementsClause: implements ClassOrInterfaceTypeList A class that includes an extends clause is called a derived class, and the class specified in the extends clause is called the base class of the derived class. When a class heritage specification omits the extends clause, the class does not have a base class. However, as is the case with every object type, type references (section 3.3.1) to the class will appear to have the members of the global interface type named 'Object' unless those members are hidden by members with the same name in the class. 110
The following constraints must be satisfied by the class heritage specification or otherwise a compile-time error occurs: If present, the type reference specified in the extends clause must denote a class type. Furthermore, the TypeName part of the type reference is required to be a reference to the class constructor function when evaluated as an expression. A class declaration may not, directly or indirectly, specify a base class that originates in the same declaration. In other words a class cannot, directly or indirectly, be a base class of itself, regardless of type arguments. The instance type (section 3.6.1) of the declared class must be assignable (section 3.10.4) to the base type reference and each of the type references listed in the implements clause. The constructor function type created by the class declaration must be assignable to the base class constructor function type, ignoring construct signatures. The following example illustrates a situation in which the first rule above would be violated: class A { a: number; } module Foo { var A = 1; class B extends A { b: string; } } When evaluated as an expression, the type reference 'A' in the extends clause doesn't reference the class constructor function of 'A' (instead it references the local variable 'A'). The only situation in which the last two constraints above are violated is when a class overrides one or more base class members with incompatible new members. Note that because <strong>TypeScript</strong> has a structural type system, a class doesn't need to explicitly state that it implements an interface—it suffices for the class to simply contain the appropriate set of instance members. The implements clause of a class provides a mechanism to assert and validate that the class contains the appropriate sets of instance members, but otherwise it has no effect on the class type. 8.1.2 Class Body The class body consists of zero or more constructor or member declarations. Statements are not allowed in the body of a class—they must be placed in the constructor or in members. ClassBody: ClassElements opt ClassElements: ClassElement ClassElements ClassElement 111
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TypeScript Language Specification V
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Table of Contents 1 Introduction ..
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4.9.1 Standard Function Expressions
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9.1 Enum Declarations .............
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1 Introduction JavaScript applicati
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1.1 Ambient Declarations An ambient
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call '$' as a function. The behavio
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function getX(p: Point) { return p.
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This TypeScript class declaration c
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Section 9 describes how programmers
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Interface definitions, like the one
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TypeScript modules provide a mechan
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2 Basic Concepts The remainder of t
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Each enum declaration has a declara
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When an identifier is resolved as a
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which infers the type of 'x' to be
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The only possible values for the Vo
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interface Array { length: number; [
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3.4 Union Types Union types represe
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3.5 Type Parameters A type paramete
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3.6 Named Types Classes, interfaces
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3.7.1 Predefined Types The any, num
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TypeMember: PropertySignature CallS
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3.7.8 Constructor Type Literals A c
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3.8.2 Call Signatures A call signat
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RestParameter: ... Identifier TypeA
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IndexSignature: [ Identifier : stri
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Type aliases are referenced using t
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o o If each type in U has an appare
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o o o M is a non-specialized call o
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3.10.5 Contextual Signature Instant
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interface List { data: T; next: Lis
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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
Page 105 and 106: function f(x: number) { if (x
Page 107 and 108: When the output target is ECMAScrip
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Page 112 and 113: An interface has the members specif
Page 114 and 115: interface Document { createElement(
Page 117: 8 Classes TypeScript supports class
Page 121 and 122: Private and protected accessibility
Page 123 and 124: interface A { x: number; f: () => v
Page 125 and 126: ConstructorOverloads: ConstructorOv
Page 127 and 128: BaseClass.apply(this, arguments); a
Page 129 and 130: Initializer expressions for instanc
Page 131 and 132: var x = A.create(); // new A() var
Page 133 and 134: MemberVariableAssignments is a sequ
Page 135 and 136: In addition, the '__extends' functi
Page 137 and 138: 9 Enums An enum type is a distinct
Page 139 and 140: An identifier or property access th
Page 141: var Color; (function (Color) { Colo
Page 144 and 145: If the declaration of 'M' above had
Page 146 and 147: module A { export interface X { s:
Page 148 and 149: module outer { var local = 1; expor
Page 150 and 151: where ModuleName is the name of the
Page 152 and 153: DeclarationElement: ExportAssignmen
Page 154 and 155: that source file is considered an e
Page 156 and 157: Unlike a non-instantiated internal
Page 158 and 159: import g = require("./geometry"); v
Page 160 and 161: 12.1.3 Ambient Class Declarations A
Page 162 and 163: An ExternalImportDeclaration in an
Page 164 and 165: PrimaryType: ParenthesizedType Pred
Page 166 and 167: 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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