This command compiles the given target, along with their dependencies,
into a Javascript source file.

Usage:
  v -b js [-options] ['run'] <target.v|target_directory> [run options]


Note that `js` defaults to the `node` codegen backend but it's also possible to
pick another:

* `js_browser`        - V outputs JS source code ready for the browser.
* `js_node`           - V outputs JS source code to run with nodejs.
* `js_freestanding`   - V outputs JS source code with no hard runtime dependency.

For more general build help, see also `v help build`.

# Interfacing the Javascript Backend code generation, passing options to it:
   -es5  Compile V to ES5 compatible code possibly shrinking output.
         Note that this flag might limit some types capabilities.
   -prod
      Do not create any JS Doc comments

   -sourcemap
      Create a source map for debugging

   -sourcemap-inline       Embed the source map directly into the
                           JavaScript source file
                           (currently default,
                           external source map files not implemented)

   -sourcemap-src-include  Include the original V source files into the
                           generated source map
   (default false, all files in the source map are currently referenced by
   their absolute system file path)

The supported targets for the JS backend are: ES6 strict
