feat: json helper now also accepts callback

Please check Readme doc for further information.

README.md

@@ -367,7 +367,7 @@ Connect-Api-Mocker also presents a bunch of helper functions to speed up writing
 - `created()`: Sets status code as 201
 - `success()`: Sets status code as 200
 - `delay(duration)`: Delays the request by given duration(in ms).
-- `json(data)`: Send given JSON object as response.
+- `json(data|callback(req,res))`: Send given JSON object as response.
 - `file(filePath)`: Responds with the content of file in given path(full path)
 - `type(contentType)`: Sets content-type header.
 - `end(body)`: Ends request and optionally sends the string output
@@ -388,6 +388,16 @@ const { delay, created, json } = require('connect-api-mocker/helpers');
 module.exports = [delay(500), created(), json({success: true})];
 ```
 
+`json` middleware also accepts a callback that has request and response objects as parameters:
+
+``js
+const { json } = require('connect-api-mocker/helpers');
+
+module.exports = [json(req => ({
+  id: req.params.userId, success: true
+}))];
+```
+
 Another example to return image as response:
 
 ```js
@@ -527,4 +537,4 @@ apiMocker('/api', {
 [webpack-dev-server]: https://github.com/webpack/webpack-dev-server
 [cra]: https://github.com/facebook/create-react-app
 [customize-cra]: https://github.com/arackaf/customize-cra
-[react-app-rewired]: https://github.com/timarney/react-app-rewired
+[react-app-rewired]: https://github.com/timarney/react-app-rewired

helpers/json.js

@@ -1,4 +1,8 @@
 module.exports = data => (req, res) => {
+  let responseData = data;
+  if (typeof data === 'function') {
+    responseData = data(req, res);
+  }
   res.setHeader('content-type', 'application/json');
-  res.end(JSON.stringify(data));
+  res.end(JSON.stringify(responseData));
 };

test/mock-helpers.spec.js

@@ -17,6 +17,16 @@ describe('Helpers', () => {
       }, done);
   });
 
+  it('json helper with callback', (done) => {
+    request(app)
+      .put('/api/users/1')
+      .expect('Content-Type', /json/)
+      .expect({
+        success: true,
+        id: '1'
+      }, done);
+  });
+
   it('notFound', (done) => {
     request(app)
       .get('/api/users')

test/mocks/helpers/users/__userId__/PUT.js

@@ -0,0 +1,8 @@
+const { json } = require('../../../../../helpers');
+
+module.exports = [
+  json(req => ({
+    success: true,
+    id: req.params.userId
+  }))
+];