allow headers to be passed as 2nd param to writeHead

src/OutgoingMessage.js

@@ -49,9 +49,16 @@ function writeHead(context, statusCode, statusMessage, headers) {
   }
 
   // 2. Status message
-  this.statusMessage = statusMessage || statusCodes[statusCode] || "unknown";
+  if (typeof statusMessage === "string") {
+    this.statusMessage = statusMessage;
+  } else {
+    this.statusMessage = statusCodes[statusCode] || "unknown";
+  }
 
   // 3. Headers
+  if (typeof statusMessage === "object" && typeof headers === "undefined") {
+    headers = statusMessage; // eslint-disable-line no-param-reassign
+  }
   if (this._headers) {
     // Slow-case: when progressive API and header fields are passed.
     if (headers) {

test/OutgoingMessage.test.js

@@ -46,6 +46,28 @@ describe("OutgoingMessage", () => {
       expect(context.res.headers).toEqual({ foo: "bar", previous: "previous" });
     });
 
+    it("Should work with a status message", () => {
+      const context = { res: {} };
+      const res = new OutgoingMessage(context);
+
+      res.writeHead(200, "baz", { foo: "bar" });
+
+      expect(res.statusMessage).toBe("baz");
+      expect(context.res.status).toBe(200);
+      expect(context.res.headers).toEqual({ foo: "bar" });
+    });
+
+    it("Should work with a headers as second parameter if no status message is given", () => {
+      const context = { res: {} };
+      const res = new OutgoingMessage(context);
+
+      res.writeHead(200, { foo: "bar" });
+
+      expect(res.statusMessage).toBe("OK");
+      expect(context.res.status).toBe(200);
+      expect(context.res.headers).toEqual({ foo: "bar" });
+    });
+
   });
 
 });