[NTG-context] How to display JavaScript's values in ConTeXt

[Zhichu Chen]

Hello everybody,

    I want to add a clock which shows the system time to a pdf file.
And I have read the ``art-calc.pdf'' and ``mwidget-p.pdf'' to find
some approaches but failed shamely. I am indeed new at ConTeXt and
JavaScript. Before I'm shocked by ConTeXt, I used LaTeX for about 2
years, so I'm confused with the conventions between ConTeXt and LaTeX.
My code is here:

----------------------------------------------------------------------------------
\setupinteraction[state=start]

\startJSpreamble functions used now
  function do_digit(d)
    { Stack[Level] += String(d);
      do_refresh(Level) }
\stopJSpreamble

\startJScode{digit}
  do_digit(JS_S_1);
\stopJScode

\definefield[Stack.1][line][Results][][

\setupfield
  [Results]
  [horizontal,frame]
  [width=fit,
   height=2cm,
   frame=on]
  [height=18pt,width=80pt,align=middle,frame=off]
  [height=18pt,width=80pt,color=red,align=right,style=type,frame=off]

\setupbuttons [background=infobutton]

\starttext

Click \button{7}[JS(digit{7})] will get
\field[Stack.1]

\stoptext
--------------------------------------------------------------------------------

I only copied these codes from "art-calc.pdf" so there must be some
other critical concepts that I haven't realized. Please point them to
me. Thanks