TypeScript Language Specification v1.5

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where ??= is one of the compound assignment operators *= /= %= += -= = >>>= &= ^= |= is subject to the same requirements, and produces a value of the same type, as the corresponding noncompound operation. A compound assignment furthermore requires v to be classified as a reference (section 4.1) and the type of the non-compound operation to be assignable to the type of v. Note that v is not permitted to be an assignment pattern in a compound assignment. 4.17.1 Destructuring Assignment A destructuring assignment is an assignment operation in which the left hand operand is a destructuring assignment pattern. AssignmentPattern: ObjectAssignmentPattern ArrayAssignmentPattern ObjectBindingPattern: { } { AssignmentPropertyList , opt } AssignmentPropertyList: AssignmentProperty AssignmentPropertyList , AssignmentProperty AssignmentProperty: Identifier Initialiser opt PropertyName : LeftHandSideExpression Initialiser opt PropertyName : AssignmentPattern Initialiser opt ArrayAssignmentPattern: [ Elision opt AssignmentRestElement opt ] [ AssignmentElementList ] [ AssignmentElementList , Elision opt AssignmentRestElement opt ] AssignmentElementList: Elision opt AssignmentElement AssignmentElementList , Elision opt AssignmentElement AssignmentElement: LeftHandSideExpression Initialiser opt AssignmentPattern Initialiser opt AssignmentRestElement: ... LeftHandSideExpression 78
In a destructuring assignment expression, the type of the expression on the right must be assignable to the assignment target on the left. An expression of type S is considered assignable to an assignment target V if one of the following is true: V is variable and S is assignable to the type of V. V is an object assignment pattern and, for each assignment property P in V, o S is the type Any, or o S has an apparent property with the property name specified in P of a type that is assignable to the target given in P, or o P specifies a numeric property name and S has a numeric index signature of a type that is assignable to the target given in P, or o S has a string index signature of a type that is assignable to the target given in P. V is an array assignment pattern, S is the type Any or an array-like type (section 3.3.2), and, for each assignment element E in V, o S is the type Any, or o S is a tuple-like type (section 3.3.3) with a property named N of a type that is assignable to the target given in E, where N is the numeric index of E in the array assignment pattern, or o S is not a tuple-like type and the numeric index signature type of S is assignable to the target given in E. In an assignment property or element that includes a default value, the type of the default value must be assignable to the target given in the assignment property or element. When the output target is ECMAScript 6 or higher, destructuring variable assignments remain unchanged in the emitted JavaScript code. When the output target is ECMAScript 3 or 5, destructuring variable assignments are rewritten to series of simple assignments. For example, the destructuring assignment var x = 1; var y = 2; [x, y] = [y, x]; is rewritten to the simple variable assignments var x = 1; var y = 2; _a = [y, x], x = _a[0], y = _a[1]; var _a; 79
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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
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 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 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 and 118: 8 Classes TypeScript supports class
Page 119 and 120: The following constraints must be s
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
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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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