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命名空间一个最明确的目的就是解决重名问题。

假设这样一种情况,当一个班上有两个名叫小明的学生时,为了明确区分它们,我们在使用名字之外,不得不使用一些额外的信息,比如他们的姓(王小明,李小明),或者他们父母的名字等等。

命名空间定义了标识符的可见范围,一个标识符可在多个名字空间中定义,它在不同名字空间中的含义是互不相干的。这样,在一个新的名字空间中可定义任何标识符,它们不会与任何已有的标识符发生冲突,因为已有的定义都处于其他名字空间中。

TypeScript 中命名空间使用 namespace 来定义,语法格式如下:

namespace SomeNameSpaceName { export interface ISomeInterfaceName { } export class SomeClassName { } }

以上定义了一个命名空间 SomeNameSpaceName,如果我们需要在外部可以调用 SomeNameSpaceName 中的类类和接口,则需要在类和接口添加 export 关键字。

要在另外一个命名空间调用语法格式为:

SomeNameSpaceName.SomeClassName;

如果一个命名空间在一个单独的 TypeScript 文件中,则应使用三斜杠 /// 引用它,语法格式如下:

/// <reference path = "SomeFileName.ts" />

以下实例演示了命名空间的使用,定义在不同文件中:

IShape.ts 文件代码:

namespace Drawing { export interface IShape { draw(); } }

Circle.ts 文件代码:

/// <reference path = "IShape.ts" /> namespace Drawing { export class Circle implements IShape { public draw() { console.log("Circle is drawn"); } } }

Triangle.ts 文件代码:

/// <reference path = "IShape.ts" /> namespace Drawing { export class Triangle implements IShape { public draw() { console.log("Triangle is drawn"); } } }

TestShape.ts 文件代码:

/// <reference path = "IShape.ts" /> /// <reference path = "Circle.ts" /> /// <reference path = "Triangle.ts" /> function drawAllShapes(shape:Drawing.IShape) { shape.draw(); } drawAllShapes(new Drawing.Circle()); drawAllShapes(new Drawing.Triangle());

使用 tsc 命令编译以上代码:

tsc --out app.js TestShape.ts  

得到以下 JavaScript 代码:

JavaScript

/// <reference path = "IShape.ts" /> var Drawing; (function (Drawing) { var Circle = /** @class */ (function () { function Circle() { } Circle.prototype.draw = function () { console.log("Circle is drawn"); }; return Circle; }()); Drawing.Circle = Circle; })(Drawing || (Drawing = {})); /// <reference path = "IShape.ts" /> var Drawing; (function (Drawing) { var Triangle = /** @class */ (function () { function Triangle() { } Triangle.prototype.draw = function () { console.log("Triangle is drawn"); }; return Triangle; }()); Drawing.Triangle = Triangle; })(Drawing || (Drawing = {})); /// <reference path = "IShape.ts" /> /// <reference path = "Circle.ts" /> /// <reference path = "Triangle.ts" /> function drawAllShapes(shape) { shape.draw(); } drawAllShapes(new Drawing.Circle()); drawAllShapes(new Drawing.Triangle());

使用 node 命令查看输出结果为:

$ node app.js
Circle is drawn
Triangle is drawn

嵌套命名空间

命名空间支持嵌套,即你可以将命名空间定义在另外一个命名空间里头。

namespace namespace_name1 { export namespace namespace_name2 { export class class_name { } } }

成员的访问使用点号 . 来实现,如下实例:

Invoice.ts 文件代码:

namespace Runoob { export namespace invoiceApp { export class Invoice { public calculateDiscount(price: number) { return price * .40; } } } }

InvoiceTest.ts 文件代码:

/// <reference path = "Invoice.ts" /> var invoice = new Runoob.invoiceApp.Invoice(); console.log(invoice.calculateDiscount(500));

使用 tsc 命令编译以上代码:

tsc --out app.js InvoiceTest.ts

得到以下 JavaScript 代码:

JavaScript

var Runoob; (function (Runoob) { var invoiceApp; (function (invoiceApp) { var Invoice = /** @class */ (function () { function Invoice() { } Invoice.prototype.calculateDiscount = function (price) { return price * .40; }; return Invoice; }()); invoiceApp.Invoice = Invoice; })(invoiceApp = Runoob.invoiceApp || (Runoob.invoiceApp = {})); })(Runoob || (Runoob = {})); /// <reference path = "Invoice.ts" /> var invoice = new Runoob.invoiceApp.Invoice(); console.log(invoice.calculateDiscount(500));

使用 node 命令查看输出结果为:

$ node app.js
200