javascript - 在 TypeScript 中动态返回一个类构造函数

Question

我正在尝试在 TypeScript 中构建一种机制，以根据表示类名称的字符串参数返回类的新实例。基本上，我正在尝试创建一个工厂，只是我不太清楚如何在 TypeScript 中执行此操作。在纯 JS 中，我可以通过将所有类构造函数存储在一个键/值对象中并调用 new ClassDictionary[className](); 来解决这个问题——这不是最可靠的解决方案，但它在这种情况下工作。我似乎无法获得类型和转换的正确组合来在 TypeScript 中完成此操作。有没有更好的办法？我在 TypeScript 中找不到工厂模式的任何示例，所以现在我只有一点 switch 语句，它丑陋且不灵活。

Answer 1

您可以为字典中的每个类添加一个函数声明，看起来像这样(访问:https://www.typescriptlang.org/docs/handbook/declaration-merging.html):

class MyClass { 
    myMethod() { return "my return"; }
}

function factory(className: "Date"): Date;
function factory(className: "Number"): Number;
function factory(className: "MyClass"): MyClass;
function factory(className: string) { 

    var ClassDictionary = {
        "Date": Date,
        "Number": Number,
        "MyClass": MyClass
    };

    return new ClassDictionary[className]();
}

var d = factory("Date");

/* Its a date. */
alert(d.toISOString());

var n = factory("Number");

/* Now a number. */
alert(n.toPrecision());

var c = factory("MyClass");

/* And now MyClass. */
alert(c.myMethod());

Playground 上的作品 ( Sample )

或者换一种方式

// ...
var ClassDictionary = { };

ClassDictionary["Date"] = Date;
function factory(className: "Date"): Date;

ClassDictionary["Number"] = Number;
function factory(className: "Number"): Number;

ClassDictionary["MyClass"] = MyClass;
function factory(className: "MyClass"): MyClass;

function factory(className: string) { 
    return new ClassDictionary[className]();
}
// ...

或带参数:

class MyClass {
    constructor(public myReturn: string) { }
    myMethod() { return this.myReturn; }
}

var ClassDictionary = { };

ClassDictionary["Date"] = Date;
function factory(className: "Date"): Date;

ClassDictionary["Number"] = Number;
function factory(className: "Number", value?: number): Number;

ClassDictionary["MyClass"] = MyClass;
function factory(className: "MyClass", myReturn: string): MyClass;

function factory(className: string, valueOrMyReturn?: number | string) { 
   if(valueOrMyReturn) return new ClassDictionary[className](valueOrMyReturn);
    return new ClassDictionary[className]();
}

var d = factory("Date");

/* Its a date. */
alert(d.toISOString());

var n = factory("Number", 42);

/* Now a number. */
alert(n.toPrecision());

var c = factory("MyClass", "This is the answer!");

/* And now MyClass. */
alert(c.myMethod());