使用TypeScript时如何处理浏览器API中的可选参数

Question

Example:

The Error constructor ( new Error([message[, fileName[, lineNumber]]]) ) has two optional parameters (fileName and lineNumber) that I would like to use but the TypeScript compiler complains with the following error message Expected 0-1 arguments, but got 3 .

What is the proper way to prevent this kind of error in TypeScript?

Answer 1

Looking at the Error documentation you linked above, I see this:

• message : Optional. A human-readable description of the error.

• fileName : Optional. The value for the fileName property on the created Error object. Defaults to the name of the file containing the code that called the Error() constructor.

• lineNumber : Optional. The value for the lineNumber property on the created Error object. Defaults to the line number containing the Error() constructor invocation.

Those big yellow warnings have the title "This API has not been standardized." (which you can see on hover). If you look at the compatibility table at the bottom of the documentation, it currently says that only Firefox supports those parameters. Other browsers and node don't.

So I guess the reason TypeScript doesn't include them in its standard library definition for the Error constructor is because it's not guaranteed to work in all JavaScript environments.

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Now if you're certain that the environment in which you will run your emitted JS code does support those parameters (ie, if you are only going to run the code in Firefox), you can use declaration merging in your own TypeScript code to add the appropriate signature:

// assuming your code is in a module, so using global augmentation here
declare global {
  interface ErrorConstructor {
    new(message?: string, fileName?: string, lineNumber?: number): Error;
  }
}

And then the compiler will not warn you:

export const iAmInAModule = true;
throw new Error("Badness happened", "badthing.js", 123); // no compiler warning now

as you wanted.

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Hope that helps; good luck!