typescript 不能在表达式打字稿中使用 new
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/41017287/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
Cannot use new with expression typescript
提问by VJAI
interface Window {
AudioContext: AudioContext;
webkitAudioContext: Function
}
let contextClass = window.AudioContext || window.webkitAudioContext;
let context: AudioContext = new contextClass();
The last line is giving me this error,
最后一行给了我这个错误，
Cannot use 'new' with an expression whose type lacks a call or construct signature
不能对类型缺少调用或构造签名的表达式使用“new”
How can I resolve this?
我该如何解决这个问题？
回答by haim770
The problem is that the compiler treats the contextClassvariable as an instanceof AudioContextwhile in fact it's merely a constructor function for an AudioContext.
问题在于编译器将contextClass变量视为 的实例，AudioContext而实际上它只是AudioContext.
You can simply use anyand the compiler will let you newit:
你可以简单地使用any，编译器会让你new：
let contextClass : any = window.AudioContext || window.webkitAudioContext;
let context: AudioContext = new contextClass();
Another option would be to introduce a Constructable<T>interface that will let you newup those types:
另一种选择是引入一个Constructable<T>接口，让您new可以使用这些类型：
interface Constructable<T> {
new(...args: any) : T;
}
interface Window
{
AudioContext: Constructable<AudioContext>;
webkitAudioContext: Constructable<AudioContext>
}
let contextClass = window.AudioContext || window.webkitAudioContext;
let context: AudioContext = new contextClass();
回答by Nathan Cooper
You can't new up an instance. new instanceofAudioContext()isn't a valid thing to do.
你不能新建一个实例。new instanceofAudioContext()不是一件有效的事情。
Your interface doesn't match the API you're trying to use. In the browser, window.AudioContextisn't a instance of AudioContext. It's the class definition method, typeof AudioContext. You'll also have the same problem with the Function.
您的界面与您尝试使用的 API 不匹配。在浏览器中，window.AudioContext不是AudioContext. 它是类定义方法，typeof AudioContext. 你也会遇到同样的问题Function。
If you'd still like to keep your interface. Try this
如果您仍然想保留您的界面。尝试这个
interface Window {
AudioContext: typeof AudioContext;
webkitAudioContext: typeof AudioContext
}
declare var window: Window;
var AudioContextDecl = window.AudioContext || window.webkitAudioContext;
var audioCtx = new AudioContext();
Or if you don't want the interface,
或者如果你不想要界面，
var AudioContextDecl = <typeof AudioContext>(window.AudioContext || window.webkitAudioContext);
var audioCtx = new AudioContext();
Or even just use any. It all transpiles to the same thing.
或者甚至只是使用any. 这一切都转化为同一件事。
