.jshintrc

contrib: switch the Windows bootstrap environment to py3.9

Use the built in `venv` module instead of `virtualenv` for simplicity, and
upgrade to a modern Mercurial that supports py3.

One issue here is that `venv` doesn't copy `python3{,Y}.dll` into the `Scripts`
subdirectory, so running the `hg.exe` that gets installed immediately fails on a
clean system because Python isn't in `PATH`.  There is code in `python.exe` to
detect when it is in a venv and add the original python install to the DLL
lookup path, which we don't do in `hg.exe` yet. The simple workaround for now is
to run the `hg` script with `python.exe`.  Typically `PYTHONLEGACYWINDOWSSTDIO`
must be set in the environment on Windows, but the clone process works without
it.

Differential Revision: https://phab.mercurial-scm.org/D11275

{
    // Enforcing
    "eqeqeq"        : true,     // true: Require triple equals (===) for comparison
    "forin"         : true,     // true: Require filtering for..in loops with obj.hasOwnProperty()
    "freeze"        : true,     // true: prohibits overwriting prototypes of native objects such as Array, Date etc.
    "nonbsp"        : true,     // true: Prohibit "non-breaking whitespace" characters.
    "undef"         : true,     // true: Require all non-global variables to be declared (prevents global leaks)

    // Environments
    "browser"       : true      // Web Browser (window, document, etc)
}