使用 TypeScript 扩展 Object.prototype

Question

我目前正在开发一个 TypeScript API，它需要一些附加功能绑定到对象原型 (Object.prototype)。

考虑以下代码：

class Foo {

}

interface Object {
    GetFoo(): Foo;
    GetFooAsString(): string;
}

//This is problematic...
Object.prototype.GetFoo = function() {
    return new Foo();
    // Note, this line is just for testing...I don't want my function to just return a blank instance of Foo!
}

//This is ok.
Object.prototype.GetFooAsString = function () {
    return this.GetFoo().toString();
}

您可能想直接在Playground 尝试此操作。

如您所见，我有一个名为Foo 的类（不是我将使用的实际对象名称）。我还扩展了Object 接口以包含两个新功能。最后，我实现了针对prototype 的函数（这些函数在纯 JavaScript 中工作，只是 TypeScript 会抱怨）。

我在哪里注释了“//这是有问题的......”TypeScript 用红色波浪线突出显示，并显示以下错误：

Cannot convert '() => Foo' to '{ (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; }': Call signatures of types '() => Foo' and '{ (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; (): Foo; }' are incompatible
() => Foo

要么这只是一个 TypeScript 错误（我知道它仍处于开发阶段，所以很多错误需要解决，我已经在 CodePlex 上说明了其中的一些），或者我遗漏了一些东西。

为什么我会遇到这个问题？

如果不是 TypeScript 错误，我该如何解决？

Answer 1

此错误已在 TS 0.9.0 alpha 中修复，如下所示：

游乐场仍在运行 0.8.3。

这基本上是因为一些关键接口（对象、数字、字符串）等上的方法被缓存作为性能优化。

如果你运行这个。第一次加载时，您不会看到该错误。 Try It。

一旦您对该代码进行了编辑，解析器就会再次检查该代码，并且由于它缓存了旧接口定义，因此会看到重复的函数定义，然后有效地崩溃了。您对该文件进行的编辑越多，错误语句就会变得越复杂。

Answer 2

我曾经有：

// See if an array contains an object
Array.prototype.contains = function (obj) {
    var i = this.length;
    while (i--) {
        if (this[i] === obj) {
            return true;
        }
    }
    return false;
}

为了使用 typescript 编译该代码，我添加了以下行：

interface Array {
    contains(obj: Object): boolean;
}

谢谢basarat！

Answer 3

我以同样的方式扩展了数组，当一个聚会使用for i in ... 循环它时遇到了一个大问题。现在您无法控制所有第三方代码，这些错误可能会非常烦人，因此我建议使用更好的方法：

interface Array<T> {
   crandom(): T;
}

/** Retrieve a random element from the list */
 Object.defineProperty(Array.prototype, 'crandom', { value: function() {

    let index = Math.floor(Math.random() * this.length);

    return this[index];
}
});

现在通过使用Object.defineProperty，您的新属性将不会被枚举，而且它是安全的。上面的代码几乎给出了数组中的一个随机元素。我也做了另一个，它从数组中弹出一个随机元素：

Object.defineProperty(Array.prototype, 'popRandom', { value: function() {

    let index = Math.floor(Math.random() * this.length);

    let result = this[index];
    this.splice(index, 1);

    return result;
}
});

使用Object.defineProperty，您可以更好地控制此创建，还可以添加其他限制。