managing repetitive code in export & tangling

[Matt Price <moptop99@gmail.com>]

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In my lectures i often have simple examples that build progressively over
several slides. In order to use klipse properly, but also for clarity, I
gneerally repeat variable declarations from slide to slide, so for
instance:

** Making Lists (Arrays)

+#NAME: js-array-historians
#+BEGIN_SRC js
let historians= ["Edward Gibbon", "Leopold von Ranke", "Edward Said", "Joan
Scott"];
#+END_SRC

** Repetition: While Loops
#+NAME: js-while-hist
#+begin_src js
<<js-array-historians>>
let i = 0;

while (i < historians.length) {
    console.log(historians[i] + " was a historian.");
    i+=1;
  }
#+end_src

There might then be a sequence of another 5 or 6 slides in which the same
"historians" array is bound to the same value and used as an example.

This works fine on its own. However, I would also like to tangle all this
code to a single file per lecture so students can download a git repo and
play with it directly in a real text editor. Unfortunately, javascript will
error out if a ~let~ bound variable is  redeclared in the same scope.  I'm
wondering if there's any way to specify that a noweb reference only be
included one time in a tangled file. Or if there are cleverer workarounds
that folks can suggest!

Thanks much,

Matt

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