418716 - JSAPI should support creating and throwing Error objects

Status: RESOLVED FIXED

(Core :: JavaScript Engine, enhancement)

Description

[Jason Orendorff [:jorendorff]]

The common JS idiom "throw new TypeError('foo: name must be a string')" doesn't have a convenient JSAPI equivalent.  The easiest thing to do is call JS_EvaluateScript, then JS_SetPendingException.  Another option is JS_GetGlobalObject, then JS_GetProperty, then a series of API calls to create arguments, then JS_ConstructObject, then JS_SetPendingException.

It would be nice to be able to do something like:

  if (!ok) {
      return JS_ThrowNewError(
          cx, JSEXN_TYPEERR,
          "foo: name must be a string");
  }

It would be especially nice to support all the standard error constructors, but *not* look them up dynamically, to avoid mysterious (or maybe malicious) behavior when a script clobbers them.

Comment 1

[Brendan Eich [:brendan]]

See also JS_GetClassObject(cx, global, JSProto_TypeError, &tyerrobj) and the like. You can get the original value of these bindings, without a property lookup if the embedding uses JSCLASS_GLOBAL_FLAGS in global's class. This is bare-bones compared to what you sketch, but I wanted to point it out in case you missed it. It is sufficient to get the constructor in order to call the constructor with the message detail arg, etc.

/be

Comment 2

[André Bargull [:anba]]

JS::CreateError(...) in https://searchfox.org/mozilla-central/source/js/public/ErrorReport.h has been added at some point, so let's close this one.