fix: Koa.js handling of node.js set error codes

lib/context.js

@@ -143,16 +143,18 @@ const proto = module.exports = {
     // force text/plain
     this.type = 'text';
 
+    let statusCode = err.status || err.statusCode;
+
     // ENOENT support
-    if ('ENOENT' === err.code) err.status = 404;
+    if ('ENOENT' === err.code) statusCode = 404;
 
     // default to 500
-    if ('number' !== typeof err.status || !statuses[err.status]) err.status = 500;
+    if ('number' !== typeof statusCode || !statuses[statusCode]) statusCode = 500;
 
     // respond
-    const code = statuses[err.status];
+    const code = statuses[statusCode];
     const msg = err.expose ? err.message : code;
-    this.status = err.status;
+    this.status = err.status = statusCode;
     this.length = Buffer.byteLength(msg);
     res.end(msg);
   },

test/context/onerror.js

@@ -100,6 +100,48 @@ describe('ctx.onerror(err)', () => {
       .expect(200, () => {});
   });
 
+  it('should set status specified in the error using statusCode', () => {
+    const app = new Koa();
+
+    app.use((ctx, next) => {
+      ctx.body = 'something else';
+      const err = new Error('Not found');
+      err.statusCode = 404;
+      throw err;
+    });
+
+    const server = app.listen();
+
+    return request(server)
+      .get('/')
+      .expect(404)
+      .expect('Content-Type', 'text/plain; charset=utf-8')
+      .expect('Not Found');
+  });
+
+  describe('when invalid err.statusCode', () => {
+    describe('not number', () => {
+      it('should respond 500', () => {
+        const app = new Koa();
+
+        app.use((ctx, next) => {
+          ctx.body = 'something else';
+          const err = new Error('some error');
+          err.statusCode = 'notnumber';
+          throw err;
+        });
+
+        const server = app.listen();
+
+        return request(server)
+          .get('/')
+          .expect(500)
+          .expect('Content-Type', 'text/plain; charset=utf-8')
+          .expect('Internal Server Error');
+      });
+    });
+  });
+
   describe('when invalid err.status', () => {
     describe('not number', () => {
       it('should respond 500', () => {