TypeScript Language Specification v1.5

More documents

Recommendations

Info

In the example var x = 1; function f(a = x) { var x = "hello"; } the local variable 'x' is in scope in the parameter initializer (thus hiding the outer 'x'), but it is an error to reference it because it will always be uninitialized at the time the parameter initializer is evaluated. 6.4 Destructuring Parameter Declarations Parameter declarations can specify binding patterns (section 3.8.2.2) and are then called destructuring parameter declarations. Similar to a destructuring variable declaration (section 5.1.2), a destructuring parameter declaration introduces zero or more named locals and initializes them with values extracted from properties or elements of the object or array passed as an argument for the parameter. The type of local introduced in a destructuring parameter declaration is determined in the same manner as a local introduced by a destructuring variable declaration, except the type T associated with a destructuring parameter declaration is determined as follows: If the declaration includes a type annotation, T is that type. Otherwise, if the declaration includes an initializer expression, T is the widened form (section 3.11) of the type of the initializer expression. Otherwise, if the declaration specifies a binding pattern, T is the implied type of that binding pattern (section 5.1.3). Otherwise, if the parameter is a rest parameter, T is any[]. Otherwise, T is any. When the output target is ECMAScript 6 or higher, except for removing the optional type annotation, destructuring parameter declarations remain unchanged in the emitted JavaScript code. When the output target is ECMAScript 3 or 5, destructuring parameter declarations are rewritten to local variable declarations. The example function drawText({ text = "", location: [x, y] = [0, 0], bold = false }) { // Draw text } declares a function drawText that takes a single parameter of the type { text?: string; location?: [number, number]; bold?: boolean; } 98
When the output target is ECMAScript 3 or 5, the function is rewritten to function drawText(_a) { var _b = _a.text, text = _b === void 0 ? "" : _b, _c = _a.location, _d = _c === void 0 ? [0, 0] : _c, x = _d[0], y = _d[1], _e = _a.bold, bold = _e === void 0 ? false : _e; // Draw text } Destructuring parameter declarations do not permit type annotations on the individual binding patterns, as such annotations would conflict with the already established meaning of colons in object literals. Type annotations must instead be written on the top-level parameter declaration. For example interface DrawTextInfo { text?: string; location?: [number, number]; bold?: boolean; } function drawText({ text, location: [x, y], bold }: DrawTextInfo) { // Draw text } 6.5 Generic Functions A function implementation may include type parameters in its signature (section 3.8.2.1) and is then called a generic function. Type parameters provide a mechanism for expressing relationships between parameter and return types in call operations. Type parameters have no run-time representation—they are purely a compile-time construct. Type parameters declared in the signature of a function implementation are in scope in the signature and body of that function implementation. The following is an example of a generic function: interface Comparable { localeCompare(other: any): number; } 99
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 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 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: function f(x: number) { if (x
Page 109: 101
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
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
Page 168 and 169:
UnaryExpression: ( Modified ) … <
Page 170 and 171:
ClassExtendsClause: extends ClassTy
Page 172 and 173:
ModuleBody: ModuleElements opt Modu
Page 174 and 175:
AmbientClassBodyElements: AmbientCl
show all

TypeScript Language Specification v1.5

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?