On Wed, Jul 10, 2013 at 12:52 PM, Domenic Denicola
<domenic at domenicdenicola.com> wrote:
> Woah, François, that seems pretty overcomplicated; why not replace everything inside the constructor with `this.message = message`? It has the same effect in the browsers I've seen. (Also don't forget `SomeError.prototype.constructor = SomeError`.)
>
> Anyway, to Jonas's point: I think `DOMError` is actually pretty OK. One thing I noticed is that the ES5 spec (and presumably ES6, although I haven't checked) is careful to never throw simple `Error` objects, but instead `TypeError`s or `RangeError`s or so on. I infer that they are leaving bare `Error` for user cases. I think "the platform" should generally follow this lead; that is, the DOM should leave bare `Error`s to the user, and throw `DOMError`s or `TypeError`s or `RangeError`s for its own errors.
>
> To answer your more general question, authors are strongly discouraged from ever throwing anything that is not `instanceof Error`, see e.g. Guillermo Rauch's [A String is not an Error](http://www.devthought.com/2011/12/22/a-string-is-not-an-error/). Also, the `name` property is generally the same across all instances of a particular error type, i.e.
>
> ```js
> errInstance.name === errInstance.constructor.name === errInstance.constructor.prototype.name === Object.getPrototypeOf(errInstance).name
> ```
>
> (You can verify this for all the built-in ES5 errors.) Usually a `code` property is used for more specific information, from what I've seen. But yes, that has to be added manually with a bit of awkwardness, i.e.
>
> ```js
> const e = new DOMError("The message");
> e.code = "TimeoutError";
> throw e;
> ```

Note that

(new DOMError) instanceof Error;

returns false. So the DOM does do the "strongly discouraged" thing. Is
this ok or bad?

Also, the DOM does not create a new class for each different value of .name.

I.e. you can get a DOMError whose .name is "NetworkError" or
"AbortError". DOMError even has a constructor which allows setting
.name to anything: new DOMError(name, message);

In fact, there are no defined situations where the DOM creates
DOMError objects whose .name is "DOMError".

Again, is this ok or is it bad practice?

/ Jonas

Note that

```js
(new DOMError) instanceof Error;
```

returns `false`. So the DOM does do the "strongly discouraged" thing. Is
this ok or bad?

Also, the DOM does not create a new class for each different value of `.name`.

I.e. you can get a `DOMError` whose `.name` is `"NetworkError"` or
`"AbortError"`. `DOMError` even has a constructor which allows setting
`.name` to anything: `new DOMError(name, message);`

In fact, there are no defined situations where the DOM creates
`DOMError` objects whose `.name` is `"DOMError"`.

Again, is this ok or is it bad practice?