Subj : Using JS_InstanceOf with jsval's
To   : netscape.public.mozilla.jseng
From : gibson@cs.utah.edu (Mike Gibson)
Date : Tue Jan 20 2004 12:59 pm

I'm having problems getting JS_InstanceOf to return what I expect when
I use jsval's returned from scripts.  I create s simple object model
with the class "A" as the parent of "B".  JS_InstanceOf then tells me
"new A();" is an instance of "B", which isn't correct.  Am I using it
right?

With the following JavaScript (test.js):

  function A() { this.a = 1; }
  function B() { this.b = 2; }
  B.prototype = new A;

I run the following C++ code (standard init code snipped):

  // Compile and run the above JavaScript
  ... snip ...

  char *s;
  jsval aval, bval;
  s = "a = new A();";
  ok = JS_EvaluateScript(cx, glob, s, strlen(s), "", 0, &aval);
  s = "b = new B();";
  ok = JS_EvaluateScript(cx, glob, s, strlen(s), "", 0, &bval);
  
  // this JS_Instance call returns true when it should return false
  JS_InstanceOf(cx, JSVAL_TO_OBJECT(aval),
                    JS_GetClass(JSVAL_TO_OBJECT(bval)), NULL));

Thanks,
Mike Gibson
gibson@cs.utah.edu

.