Use an objects own property, or an environment variable. Optionally treat as a boolean if the env should be set to 1 or 0.
ownOrEnv(object, field, env, boolean)
Use the object[field] if it's an own property, otherwise use the
named environent variable. If boolean is set to true, then cast
to a boolean flag.
// will set doTheThing to true based on config.doThing, falling back
// to reading process.env.DO_THING, where '0' is treated as false.
var doTheThing = ownOrEnv(config, 'doThing', 'DO_THING', true)
// just treat this one as a string, not a boolean flag
var file = ownOrEnv(config, 'file', 'MY_FILE')