feat: expand scenarios covered by default arguments for environments

[shadowspawn]

Problem

We are proposing to determine appropriate default arguments for node --eval, Electron, and ES6.

Using require.main to determine --eval (or REPL) gives false positive for ES6 main program.

Related: #5 #18

Solution

Implement a placeholder for process.mainArgs that covers the scenarios that have been raised.

• detect node --eval directly by checking options passed to node (-e, --eval)
• detect node --print directly by checking options passed to node (-p, --print)
• no need to detect REPL because no user arguments from CLI?
• test for bundled Electron app (using same approach as Yargs and Commander)
• fallback to usual process.argv.slice(2)

Related PRs for Electron argument processing:

• https://github.com/tj/commander.js/pull/1172/files
• https://github.com/yargs/yargs/pull/1554/files

And for historical interest, the addition of defaultApp in Electron to work-around the variant behaviour:

• process.argv differs in built electron apps electron/electron#4690 (comment)

Example

% node -e 'console.log(require(".").parseArgs())' 1 --foo 2 3
{
  args: { foo: true },
  values: { foo: [ undefined ] },
  positionals: [ '1', '2', '3' ]
}

 % node es6.mjs --foo 1 2 3
{
  args: { foo: true },
  values: { foo: [ undefined ] },
  positionals: [ '1', '2', '3' ]
}

[shadowspawn]

Just spotted node -p in a comment. I had a feeling I was missing another special mode!

nodejs/node#35015 (comment)

[ljharb]

node -pe is critical

[shadowspawn]

Added -p and --print. e.g.

% node --print 'require (".").parseArgs()' first second
{ args: {}, values: {}, positionals: [ 'first', 'second' ] }

[shadowspawn]

Added tests, refactored code to be an explicit placeholder for process.mainArgs, describe Election as an example rather than as intended for inclusion.