An ESLint formatter which display statistics for errors and warnings, but outputs only detailed information about errors.

errorOnlyEsLintFormatter.js

/**
 * An ESLint formatter which shows only errors. Warnings are displayed only in form of an aggregated
 * total number.
 *
 * Example Output: Only Warnings:
 *
 * >
 * > ✖ 98 problems (0 errors, 98 warnings)
 * >
 *
 * Example Output: Errors and Warnings:
 * 
 * >
 * >  /files/index.js
 * >  1:1  error  Expected indentation of 1 tab character but found 0  indent
 * >
 * > ✖ 99 problems (1 error, 98 warnings)
 * >
 */

var defaultFormatter = require('./node_modules/eslint/lib/formatters/stylish');
var chalk = require('chalk');
var crossIcon = '\u2716';

function pluralize(word, count) {
	return (count === 1 ? word : word + "s");
}

module.exports = function(results) {
	var output = '\n';
	var errorResults = [];
	var total = 0;
	var numberOfWarnings = 0;
	var numberOfErrors = 0;
	var errorOutput;

	if(results.length === 0) { return ''; }

	results.forEach(function(result) {
		var errorMessages;

		if(result.fatal) {
			errorResults.push(result);
			return;
		}

		errorMessages = result.messages.filter(function(message) { return message.severity === 2; });
		total += result.messages.length;
		numberOfErrors += errorMessages.length;
		numberOfWarnings += result.messages.length - errorMessages.length;

		if(errorMessages.length > 0) {
			errorResults.push(Object.assign({}, result, { messages: errorMessages }));
		}
	});

	if(errorResults.length > 0) {
		errorOutput = defaultFormatter(errorResults);
		output += errorOutput.substr(0, errorOutput.lastIndexOf(crossIcon));
	}

	output += chalk[numberOfErrors > 0 ? 'red' : 'yellow'].bold([
		crossIcon, ' ', total, pluralize(' problem', total),
		' (', numberOfErrors, pluralize(' error', numberOfErrors), ', ',
		numberOfWarnings, pluralize(' warning', numberOfWarnings), ')\n'
	].join(''));

	return output;
};