A11y: support NO_COLOR environment variable in output

[MaddyGuthridge]

Resolves #302

This is a quick fix, rather than a major change to the system Morgan uses for styled console output. In an ideal world, using NO_COLOR would disable all styling of output, which would remove the presence of control characters in things like CI logs. Currently, this PR just sets the color to 0 if NO_COLOR is set in process.env, which is acceptable for accessibility.

As a side note: I'm not used to writing code for such old versions of Node, so apologies if I made any mistakes that break that compatibility. I tried testing using Node 0.8.28, but was unable to get npm i to work correctly. Let me know if I broke anything and I'll do my best to fix it up :)

• Implementation
• Test suite passes with 100% coverage
• Linting passes with no errors or warnings

I accept the certificate of origin, and am happy for my contribution to use the project's MIT software license.

[krzysdz]

I believe that NO_COLOR=1 should entirely remove the colour-related ANSI escape codes instead of emitting the reset sequence.

[MaddyGuthridge]

Makes sense to me, although that would require a bit of a bigger refactor. I am pretty flat-out right now so probably won't have time to sort that out for a few weeks at least. I'll keep it on my todo list though.

[krzysdz]

I have an idea that may be a little weird, but should work - after the current 'dev' format (in line 233) add something like

/**
 * NO_COLOR override of dev
 */

if (process.env.NO_COLOR) {
  morgan.format('dev', ':method :url :status :response-time ms - :res[content-length]')
}

It assumes that the NO_COLOR env var will be set before requiring morgan, which should be the case most of the time (this may cause problems with tests, as the relevant tests would have to import morgan separately). This should work, because morgan.format() performs a simple assignment, so calling it with the same name overwrites the previous format (this causes some problems as .format() and .token() can overwrite all morgan properties - #265):

morgan/index.js

Lines 480 to 491 in bd171d7

	/**
	* Define a format with the given name.
	*
	* @param {string} name
	* @param {string|function} fmt
	* @public
	*/
	function format (name, fmt) {
	morgan[name] = fmt
	return this
	}

Alternatively, the developmentFormatLine and the string with no escape sequences could be stored as variables and set as the dev format when instantiating morgan somewhere above

morgan/index.js

Lines 107 to 110 in bd171d7

	// format function
	var formatLine = typeof fmt !== 'function'
	? getFormatFunction(fmt)
	: fmt

This would make testing easier, but IMO would negatively impact the code structure (suddenly one format is defined inside morgan(), not with other formats, and uses separate variables).

@jonchurch @UlisesGascon do you think this would be an acceptable solution?

[UlisesGascon]

Based on #303 (comment), I think that #372 supperseeds this pr 🤔