TypeScript Language Specification v1.5

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RestParameter: ... Identifier TypeAnnotation opt A parameter declaration may specify either an identifier or a binding pattern (5.1.2). The identifiers specified in parameter declarations and binding patterns in a parameter list must be unique within that parameter list. The type of a parameter in a signature is determined as follows: If the declaration includes a type annotation, the parameter is of that type. Otherwise, if the declaration includes an initializer expression (which is permitted only when the parameter list occurs in conjunction with a function body), the parameter type is the widened form (section 3.11) of the type of the initializer expression. Otherwise, if the declaration specifies a binding pattern, the parameter type is the implied type of that binding pattern (section 5.1.3). Otherwise, if the parameter is a rest parameter, the parameter type is any[]. Otherwise, the parameter type is any. A parameter is permitted to include a public, private, or protected modifier only if it occurs in the parameter list of a ConstructorImplementation (section 8.3.1) and only if it doesn't specify a BindingPattern. A type annotation for a rest parameter must denote an array type. When a parameter type annotation specifies a string literal type, the containing signature is a specialized signature (section 3.8.2.4). Specialized signatures are not permitted in conjunction with a function body, i.e. the FunctionExpression, FunctionImplementation, MemberFunctionImplementation, and ConstructorImplementation grammar productions do not permit parameters with string literal types. A parameter can be marked optional by following its name or binding pattern with a question mark (?) or by including an initializer. Initializers (including binding property or element initializers) are permitted only when the parameter list occurs in conjunction with a function body, i.e. only in a FunctionExpression, FunctionImplementation, MemberFunctionImplementation, or ConstructorImplementation grammar production. 3.8.2.3 Return Type If present, a call signature's return type annotation specifies the type of the value computed and returned by a call operation. A void return type annotation is used to indicate that a function has no return value. When a call signature with no return type annotation occurs in a context without a function body, the return type is assumed to be the Any type. When a call signature with no return type annotation occurs in a context that has a function body (specifically, a function implementation, a member function implementation, or a member accessor declaration), the return type is inferred from the function body as described in section 6.3. 44
3.8.2.4 Specialized Signatures When a parameter type annotation specifies a string literal type (section 3.2.8), the containing signature is considered a specialized signature. Specialized signatures are used to express patterns where specific string values for some parameters cause the types of other parameters or the function result to become further specialized. For example, the declaration interface Document { createElement(tagName: "div"): HTMLDivElement; createElement(tagName: "span"): HTMLSpanElement; createElement(tagName: "canvas"): HTMLCanvasElement; createElement(tagName: string): HTMLElement; } states that calls to 'createElement' with the string literals "div", "span", and "canvas" return values of type 'HTMLDivElement', 'HTMLSpanElement', and 'HTMLCanvasElement' respectively, and that calls with all other string expressions return values of type 'HTMLElement'. When writing overloaded declarations such as the one above it is important to list the non-specialized signature last. This is because overload resolution (section 4.12.1) processes the candidates in declaration order and picks the first one that matches. Every specialized call or construct signature in an object type must be assignable to at least one nonspecialized call or construct signature in the same object type (where a call signature A is considered assignable to another call signature B if an object type containing only A would be assignable to an object type containing only B). For example, the 'createElement' property in the example above is of a type that contains three specialized signatures, all of which are assignable to the non-specialized signature in the type. 3.8.3 Construct Signatures A construct signature defines the parameter list and return type associated with applying the new operator (section 4.11) to an instance of the containing type. A type may overload new operations by defining multiple construct signatures with different parameter lists. ConstructSignature: new TypeParameters opt ( ParameterList opt ) TypeAnnotation opt The type parameters, parameter list, and return type of a construct signature are subject to the same rules as a call signature. A type containing construct signatures is said to be a constructor type. 3.8.4 Index Signatures An index signature defines a type constraint for properties in the containing type. 45
Page 1 and 2: 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 54 and 55: IndexSignature: [ Identifier : stri
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
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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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