Allow setting support level with FORCE_COLOR environment variable

index.js

@@ -15,8 +15,18 @@ if (hasFlag('no-color') ||
 	hasFlag('color=always')) {
 	forceColor = true;
 }
+let forceLevel;
 if ('FORCE_COLOR' in env) {
-	forceColor = env.FORCE_COLOR.length === 0 || parseInt(env.FORCE_COLOR, 10) !== 0;
+	if (env.FORCE_COLOR === true || env.FORCE_COLOR === 'true') {
+		forceColor = true;
+	} else if (env.FORCE_COLOR === false || env.FORCE_COLOR === 'false') {
+		forceColor = false;
+	} else {
+		forceLevel = env.FORCE_COLOR.length === 0 ?
+			1 :
+      parseInt(env.FORCE_COLOR, 10);
+		forceColor = forceLevel !== 0;
+	}
 }
 
 function translateLevel(level) {
@@ -47,6 +57,10 @@ function supportsColor(stream) {
 		return 2;
 	}
 
+	if (forceLevel !== undefined) {
+		return forceLevel;
+	}
+
 	if (stream && !stream.isTTY && forceColor !== true) {
 		return 0;
 	}

test.js

@@ -317,3 +317,35 @@ test('return level 2 when FORCE_COLOR is set when not TTY in xterm256', t => {
 	t.truthy(result.stdout);
 	t.is(result.stdout.level, 2);
 });
+
+test('supports setting a color value using FORCE_COLOR', t => {
+	let result;
+	process.env.FORCE_COLOR = '2';
+	result = importFresh('.');
+	t.truthy(result.stdout);
+	t.is(result.stdout.level, 2);
+
+	process.env.FORCE_COLOR = '3';
+	result = importFresh('.');
+	t.truthy(result.stdout);
+	t.is(result.stdout.level, 3);
+});
+
+test('FORCE_COLOR works when set via command line (all values are strings)', t => {
+	let result;
+	process.env.FORCE_COLOR = 'true';
+	result = importFresh('.');
+	t.truthy(result.stdout);
+	t.is(result.stdout.level, 1);
+
+	process.stdout.isTTY = false;
+	process.env.FORCE_COLOR = 'true';
+	process.env.TERM = 'xterm-256color';
+	result = importFresh('.');
+	t.truthy(result.stdout);
+	t.is(result.stdout.level, 2);
+
+	process.env.FORCE_COLOR = 'false';
+	result = importFresh('.');
+	t.false(result.stdout);
+});