feat: stringify err object on non-error (#36)

The `err` may be an object and the error message would print as `nodejs.Error: non-error thrown: [object Object]` which is not helpful, try to stringify it.

index.js

@@ -36,7 +36,14 @@ module.exports = function onerror(app, options) {
 
  // wrap non-error object
  if (!(err instanceof Error)) {
- const newError = new Error('non-error thrown: ' + err);
+ let errMsg = err;
+ if (typeof err === 'object') {
+ try {
+ errMsg = JSON.stringify(err);
+ // eslint-disable-next-line no-empty
+ } catch (e) {}
+ }
+ const newError = new Error('non-error thrown: ' + errMsg);
  // err maybe an object, try to copy the name, message and stack to the new error instance
  if (err) {
  if (err.name) newError.name = err.name;

test/json.test.js

@@ -71,7 +71,7 @@ describe('json.test.js', () => {
  .expect({ error: 'Internal Server Error' }, done);
  });
 
- it('should wrap non-error object', done => {
+ it('should wrap non-error primitive value', done => {
  const app = new koa();
  app.on('error', () => {});
  onerror(app);
@@ -86,6 +86,21 @@ describe('json.test.js', () => {
  .expect({ error: 'non-error thrown: 1' }, done);
  });
 
+ it('should wrap non-error object and stringify it', done => {
+ const app = new koa();
+ app.on('error', () => {});
+ onerror(app);
+ app.use(() => {
+ throw { error: true };
+ });
+
+ request(app.callback())
+ .get('/')
+ .set('Accept', 'application/json')
+ .expect(500)
+ .expect({ error: 'non-error thrown: {"error":true}' }, done);
+ });
+
  it('should wrap mock error obj instead of Error instance', done => {
  done = pedding(2, done);
  const app = new koa();