Respect NO_COLOR environment variable in the dev format

README.md

@@ -168,6 +168,10 @@ for information codes.
 GET /dev 200 0.224 ms - 2
 ```
 
+Set the `NO_COLOR` environment variable to a non-empty value to disable the
+colored output (see [no-color.org](https://no-color.org/)). The same fields are
+then printed without any ANSI escape sequences.
+
 ##### short
 
 Shorter than default, also including response time.

index.js

@@ -211,6 +211,15 @@ morgan.format('tiny', ':method :url :status :res[content-length] - :response-tim
  */
 
 morgan.format('dev', function developmentFormatLine (tokens, req, res) {
+  // NO_COLOR (https://no-color.org/): when present and not an empty
+  // string, regardless of its value, ANSI color codes must not be added
+  if (process.env.NO_COLOR) {
+    var plainFn = developmentFormatLine.plain || (developmentFormatLine.plain =
+      compile(':method :url :status :response-time ms - :res[content-length]'))
+
+    return plainFn(tokens, req, res)
+  }
+
   // get the status code if response written
   var status = headersSent(res)
     ? res.statusCode

test/morgan.js

@@ -1523,6 +1523,38 @@ describe('morgan()', function () {
             .expect(200, cb)
         })
       })
+
+      describe('with NO_COLOR environment variable set', function () {
+        beforeEach(function () {
+          process.env.NO_COLOR = '1'
+        })
+
+        afterEach(function () {
+          delete process.env.NO_COLOR
+        })
+
+        it('should not emit any ANSI escape codes', function (done) {
+          var cb = after(2, function (err, res, line) {
+            if (err) return done(err)
+            assert.strictEqual(line.indexOf('\x1b'), -1)
+            assert.ok(/^GET \/ 200 \d+\.\d{3} ms - -$/.test(line), 'unexpected line: ' + line)
+            done()
+          })
+
+          var stream = createLineStream(function onLine (line) {
+            cb(null, null, line)
+          })
+
+          var server = createServer('dev', { stream: stream }, function (req, res, next) {
+            res.statusCode = 200
+            next()
+          })
+
+          request(server)
+            .get('/')
+            .expect(200, cb)
+        })
+      })
     })
 
     describe('short', function () {