TypeScript 命名空间
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命名空间中定义,它在不同命名空间中的含义是互不相干的。这样,在一个新的命名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命名空间中。
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
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