ts 命名空间

1. 命名空间 **namespace**
2. ts 中命名空间使用 **namespace** 来定义
3. ts 命名空间用于解决重名问题
4. 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
5. 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
6. 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
7. 如果一个命名空间在一个单独的 ts 文件中，则应使用三斜杠 **///** 引用它
8. 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

// IShape.ts
namespace Drawing {
  export interface IShape {
    draw();
  }
}

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

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

// TestShape.ts
/// <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());
// Circle is drawn
// Triangle is drawn

输入 tsc --out app.js TestShape.ts 编译生成结果 app.js，然后再使用 node 命令 node .\app.js 来执行编译结果。

编译后得到的 app.js 文件内容如下：

// Circle.ts
/// <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 = {}));
// Triangle.ts
/// <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 = {}));
// TestShape.ts
/// <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());
// Circle is drawn
// Triangle is drawn

// Invoice.ts
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));
// 200