Memory leak when closing over ObjectTemplate reference

[mnutt]

This is the simplest reproduction of an issue I'm seeing in a larger project, where my app is leaking memory even after the context is closed and the isolate is disposed.

The obvious answer would be "don't close over global, use info.Context().Global() or something". But in the more complex reproduction (pprof/leak check) I don't believe it's possible, since I'm hoping to provide a jquery-ish JS api similar to this:

const parser = htmlParser(htmlBody); // go function that instantiates an HtmlParser struct and returns reference
const items = parser.find(".item"); // uses instantiated HtmlParser to return an HtmlParserSelection struct
return items.map(i => i.attr("src"); // HtmlParserSelection iterates over found objects

This requires js to temporarily retain a reference to a go struct, which I believe comes down to needing a v8.FunctionCallback to reference a v8.ObjectTemplate created outside of it.

[codecov]

Codecov Report

Merging #286 (71fcd86) into master (5e91d3d) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #286   +/-   ##
=======================================
  Coverage   95.86%   95.86%           
=======================================
  Files          17       17           
  Lines         580      580           
=======================================
  Hits          556      556           
  Misses         15       15           
  Partials        9        9           

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