TypeScript 基础教程

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:

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

/// <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:

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

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