0.1.3 • Public • Published

Simple JSON Replay Server ❤️ Build Status npm version Node version

Pefect companion with single page application development, and unit mock testing. Especially designed for angularjs 1 and 2 & reactjs. Zero Code invasion to your production code.

It is not a Restful Json Server

Have you spent a lot of time trying to find a simple straight-forward file based json replay server which will return json responses by matching some simple filtering criteria in requested parameters (such as query, headers, post body etc)?

You probably will be disappointed, because not all but at least majority of them are fancy shinning restful style severs which either returning dynamic json in memory or manipulate some text based db files. And obviously, they will all require you to send standard restful style requests and then response with some dynamic results which you might have to think hard to set it up.

Isn't it overkill? if we just need a mock server for development and unit testing. Or, if you have legacy backend API design, which are not strictly following restful URL patterns.

Simple Features

  • Decoupled with production code This json replay server will run only side by side in local development/testing environment on demand, Zero code change required in your production code.
  • Simple command to launch it with optional port and folder configuration.
  • Supre Easy to create & maintain data Create a pure json file in your replay data folder and you should get it right away, no programming is required.
  • Advanced features to allow you set more matching rules including query parameters, method, header, body, cookie etc.
  • Straight-foward rules configured in the file, they are almost self explaining.
  • Fast & Predictable, Once configured, it will response immediately and consistently.
  • Simple but still Powerful, You can configure different rules to simulating different responses to cover different scenarios for the same service call, such as paginiation, error, failure etc.

Node Dependency

Support node version >= 4.0.0 by not using any ES6 syntax for a period of time.

How to start

Install to your package.json

npm install simple-json-replay-server --save-dev

Create app_mock folder under your application root

go to your application root folder, where it has package.json & your node_modules folder.

mkdir app_mock

Create mock data config files

Create below json files, put them inside of app_mock folder, you can create any layer of sub folders to organize your mock data files. The mock server will only look for files ending with ".json" in app_mock folder recursively.

Please note: you are able to config a different port number if it conflicts.


    "comment" : "You are free to add comment for this json mock response, comment filed is optional",
    "request" : {
        "path": "test",
        "method" : "get"
    "response" : {
        "status" : 200,
        "data" : {
            "message" : "You get this message when you hit http://localhost:8008/test or http://localhost:8008/test?anyParameter=anyValue&anyParameter2=anyValue2 as long as you don't include 'param1=value1'"


    "comment" : "",
    "request" : {
        "path": "test",
        "method" : "get",
        "query" : {
            "param1" : "value1"
    "response" : {
        "status" : 200,
        "data" : {
            "message" : "You get this message when you hit http://localhost:8008/test&param1=value1 or with additional parameters as long as you have 'param1=value1'"

So, you could imagine that you can config json data with multiple level of filtering conditions. thus, you could possible to define a default mock response for a use case, then define more strict rules to return another mock data based on parameter/body/header changes.

Some Sample Use Cases

Some More Mock Configurations Examples

Start the replay server

node node_modules/simple-json-replay-server/src/main.js

Config a shortcut in package.json

Nice to have step only, you can create alias in mac/unix or bat file for windows instead.

Open package.json of your frontend application

  "scripts": {
    "mockServer": "node node_modules/simple-json-replay-server/src/main.js"

Now, you can run below shorter command to start mock server

npm run mockServer

You can then create concurrent tasks in whatever preferrable ways you want

Mock Data Specification

✦ Request (Filtering Rules)

The request object can be defined as described in below table.

You can define more than one mock data which are mapping to the same path. And then, you should define different filtering rules which can narrow down the results.

However, if more than one mock data match the same number of filtering criteria (for query/body, each key is consider as seperate criteria), we will not guarantee which mock data will be returned.

Key Value Optional Description
path part of path or full path No You can give partial of path or full path, for example, the full path is "/api/examples", you can give just "examples" or "example" or "api/examples", all of them will match.
method http methods Yes Default as get
query key value pairs Yes Default as undefined (no filtering). You can think about this is a filtering logic. As long as you defined one or more key-value pairs, it will only return results which exactly matching these query parameters to pass through. If multiple results all matching, it will choose the first one.
body a json map Yes Default as undefined. you can have partial values in multiple layers, it will only try to match partial branch of the value till the end. So far, only support json body (application/json) & form-urlencoded (application/x-www-form-urlencoded) when post.
headers key value pairs Yes default as undefined. Similiar to query, if you add any thing in here, it will filter out the data with headers having specific value.
cookies key value pairs Yes default as undefined. Similiar to headers, if you add any thing in here, it will filter out the data with cookies having specific value. (Do not support secured cookies for now)

✦ Response

The Response object can be defined as below properties.

Key Value Optional Description
status http status Yes default as 200
delay number in milliseconds Yes default as 0 which is no delay. you can give negative value, which means timeout, in this case, will ignore the any other response settings.
data a json object map Yes you can define the expected json response.
html a string Yes When you define html as response, please note that you should not define data, if both data & html are defined, it will consider only data.
file a json object map Yes it support two keys, filePath the file that you want user to download, it should be a relative path to config file including original file name, downloadFilename is the file name that you want browser to use when download. please refer to for details.
location a relative path or an absolute url yes Used to mock 302 forwarding behavior, when you set location, your status code has to be set as 302, and this key can not be used with data/html/file.

Integrate with your development work flow

As we all know, nowadays, most of frontend projects have been completely seperated from backend projects.

When we develop frontend application, we often tend to mock the data either directly in the code or hard-coded in backend service before implemented, which will requires some code changes during integration phase. And more often it is not easy to setup mock data which can cover many business scenarios.

With this simple json replay server approach, your code is always the same code which you will use in production, and in local development environment, you can route all your backend restful service calls to this replay server and thus you can run and play with your frontend application without ANY dependency on your backend server.

I will take below some of most popular frontend build tools/solutions for example:

  • Webpack
  • Grunt (Gulp as well)

✦ Webpack

Webpack based solution is gaining more popularity, and both angular 2 official and one of most popular tools - angular-cli are all using webpack as their build tool.

► Angular2 with Angular-Cli

Please find instruction in below

Original source:

Using the proxying support in webpack's dev server we can highjack certain urls and send them to a backend server. We do this by passing a file to --proxy-config

Say we have a server running on http://localhost:8008/api and we want all calls to http://localhost:4200/api to go to that server.

We create a file next to projects package.json called proxy.conf.json with the content

  "/api/**": {
    "target": "http://localhost:8008",
    "secure": false

You can read more about what options are available here webpack-dev-server proxy settings

and then we edit the package.json file's start script to be

"startWithMock": "ng serve --proxy-config proxy.conf.json",

now run it with npm startWithMock

► Directly Use Webpack

Very similiar to angular-cli configuration because it is using the same webpack which then use webpack-dev-server internally.

You should add below configuration in your webpack.config.js in your project.

Please note: this is a javascript file instead of json file.

An example of this javascript based configuration file for webpack:

//shortcut config
proxy: {
  "/api": "http://localhost:8008"

This is almost equivalent to

proxy: {
  "/api": {
    target: "http://localhost:8008",
    secure: false

For more advanced proxy configuration, please read offical document:

✦ Grunt

If your project is still using grunt or gulp, you can look at this charpter. I will not give example for gulp, however, the approach would be very much similiar.

Although you can use grunt-contrib-connect with some magic middleware settings to make it work, I would suggest you to use grunt-connect-proxy plug-in which kind simplify the configurations.

You can find more details in here:

    connect: {
        server: {
            options: {
                port: 9000,
                hostname: 'localhost'
            proxies: [
                    context: '/api',
                    host: '',
                    port: 8008,
                    https: false

Release Note

Version Description
0.0.10 Include body mapping for json body (application/json) & form-urlencoded (application/x-www-form-urlencoded)
0.0.11 support filtering by headers value.
0.0.12 support new response type as html
0.1.0 support file download, new response type as file
0.1.2 support 302 forwarding with a location (relative path or absolute path)
0.1.3 support support cookie matching




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