Subj : Help with scoping within the JSAPI
To   : netscape.public.mozilla.jseng
From : alipman2@yahoo.com
Date : Fri May 27 2005 01:44 pm

I am writing an application where I need 3 levels of scoping.

1.   Application Scope
2.   Global Scope
3.   Local Scope

Currently, I have 2 levels of scoping working
I use the Global Object for scope 1, and then I push a stack frame with
my own varobj for scope 2.


  ////////////////////////////////////////////////
  At the beginning of execution I create my own Frame.
  ////////////////////////////////////////////////


    JSStackFrame *m_fp;
    JSStackFrame m_Frame;

  memset( (void *)&m_Frame,0 ,sizeof( m_Frame));
  m_Frame.varobj = m_glob;
  m_Frame.fun = NULL;
  m_Frame.thisp = m_glob;
  m_Frame.argc = m_Frame.nvars = 0;
  m_Frame.argv = m_Frame.vars = NULL;
  m_Frame.annotation = NULL;
  m_Frame.sharpArray = NULL;
  m_Frame.rval = JSVAL_VOID;
  m_Frame.down = NULL;
  m_Frame.scopeChain = m_glob;
  m_Frame.pc = NULL;
  m_Frame.sp =  NULL;
  m_Frame.spbase = NULL;
  m_Frame.sharpDepth = 0;
  m_Frame.flags = 0;
  m_Frame.dormantNext = NULL;
  m_Frame.objAtomMap = NULL;

  m_fp=&m_Frame;

  ////////////////////////////////////////////////
  I use the following code to execute code using this frame.
  ////////////////////////////////////////////////


  if (!js_Execute(m_cx, m_fp->scopeChain, m_ExecutingScript, m_fp, 0,
&ScriptResult)) {
#if JS_HAS_EXCEPTIONS
      js_ReportUncaughtException(m_cx);
#endif
    ok = JS_FALSE;
  }
  else {
    ok = JS_TRUE;
  }


  ////////////////////////////////////////////////
  I use the following code to push a stack frame to go to scope 2.  I
adapted this code from the code
 that pushes on a stack frame before a function is called.
m_ScopeLevel is a global variable
  ////////////////////////////////////////////////

  uintN nframeslots;
  void *newmark;
  JSInlineFrame *newifp;
  jsval *sp, *newsp;
  JSStackFrame *fp;
  jsval *vp;

  if (   m_ScopeLevel > 0 ) {
    m_ErrorMessage ="Push has already been executed";
    return false;
  }
  fp = NULL;
  /* Compute the number of stack slots needed for fun. */
  nframeslots = (sizeof(JSInlineFrame) + sizeof(jsval) - 1)
    / sizeof(jsval);

  /* Allocate the frame and space for vars and operands. */
  newsp = js_AllocRawStack(m_cx, nframeslots , &newmark);
  if (!newsp) {
    m_ErrorMessage = "js_AllocRawStack failed";
    return false;
  }
  newifp = (JSInlineFrame *) newsp;
  newsp += nframeslots;
  vp = sp - 2;

  JSObject *varobj;
  varobj = JS_NewObject(m_cx, &global_class, NULL, NULL);
  if (!varobj) {
    m_ErrorMessage="Couldn't create variables object";
    return false;

  if ( JS_AddRoot(m_cx, varobj) ) {
    m_ErrorMessage="Can't root scope object";
    return false;
  }

  }
  JS_SetGlobalObject(m_cx, varobj);
  if (!JS_InitStandardClasses(m_cx, varobj)) {
    m_ErrorMessage="Initialization Error, Can't Init Standard Classes";
    return false;
  }
  /* Initialize the stack frame. */
  memset(newifp, 0, sizeof(JSInlineFrame));
  newifp->frame.rval = JSVAL_VOID;
  newifp->frame.nvars = 0;
  newifp->frame.vars = newsp;
  newifp->frame.argv = vp + 2;
  newifp->frame.scopeChain = varobj;
  newifp->mark = newmark;
  newifp->frame.down = m_fp;
  newifp->frame.argsobj=NULL;
  newifp->frame.varobj = varobj;


  /* Push void to initialize local variables. */
  sp = newsp;
  newifp->frame.spbase = sp;
  SAVE_SP(&newifp->frame);
  m_fp = &newifp->frame;
  m_ScopeLevel++;
  return true;

  /////////////////////////////////////////////////
  I use the following code to pop the stack frame
  ////////////////////////////////////////////////

  JSStackFrame *fp;
  JSInlineFrame *ifp = (JSInlineFrame *) m_fp;
  jsval *vp;
  jsval *sp;


  if ( m_ScopeLevel == 0 ) {
    m_ErrorMessage="PopScope called with no corresponding PushScope";
    return false;
  }


  /* Restore cx->fp and release the inline frame's space. */
  fp = m_fp;

  if ( !JS_RemoveRoot(m_cx, fp->varobj)){
    m_ErrorMessage="Couldn't not remove scope object from root";
  }

  sp = fp->spbase;
  m_cx->fp = fp = fp->down;
  m_fp = fp;
  JS_ARENA_RELEASE(&m_cx->stackPool, ifp->mark);

  if ( fp ) {
    vp = fp->argv - 2;
    fp->sp = vp + 1;
    RESTORE_SP(fp);
  }
  m_ScopeLevel--;
  return true;
}




  ////////////////////////////////////////////////

  If I want to push another level of stack frame, what do I set in the
new frame that I create?

.