A simple Node.js REST server simulator for Testing

You are developing a client application (Angular / React etc.) and you need to receive the data from a REST API service.
Often you don’t have the access to the remote service or it doesn’t have the required data for your tests (dynamically generated data).

A direct access to a test .json file is not possible from the client because of security restrictions of the browser (the browser should not be able to play with the filesystem).

Solution – Concept

A client app can request (GET) a predefined page to a local server and receive the JSON file for the test.
The server can be implemented in Node.js and it serves static files content as response to http requests.

Solution – Implementation

The code and the installation procedure are here: https://github.com/marco76/node_rest_server/

The structure of the code is very simple:

Here an example of response:

Solution – Details

The file server.js create a new http server and waits for http requests.
It instantiates a loaderModule that contain the class that will retrieve the JSON data.

// import the function from the module 
    var loaderModule = require('./ResponseLoader.js'); 
    // create an instance of the prototype 
    var loader = new loaderModule("loader"); 
 
    function requestService(request, response){ 
        // url == filename without extension  
        var url = request.url; 
         
        // home page called 
        if (url=="/"){ 
            url = "/index"; 
        } 
         
        // call the method that load the static page  
        loader.load(url); 
         
        // prepare the http response 
        response.statusCode = 200; 
        response.setHeader('Content-Type', 'application/json'); 
        // add the JSON content 
        response.end(loader.getJson()); 
    }

The second important JavaScript file is the function that receives the request to load a file and retrieves the content:

function ResponseLoader (name){ 
 
    // the content of the file is stored in this variable 
    var json; 
 
    // method that load the file on the base of the URL 
    ResponseLoader.prototype.load = function(url){ 
        console.log("requested file: " + url); 
        // url: hello -> file: [current directory]/json/hello.json 
        fs.readFile( __dirname + '/json' +url+'.json', function (err, data) { 
            if (err) { 
                console.log('error'); 
                throw err; 
            } 
            // the content of the file is assigned to the variable 
            json = data; 
 
            console.log(name + " : " +data.toString()); 
        }) 
    }; 
 
    // give me the json content 
    ResponseLoader.prototype.getJson = function (){ 
        console.log(name + " : return json"); 
 
        return json; 
    }; 

The features are very basic but they can be easily extended. The code is modularized using the ‚module‘ feature of node.js.

If you come from Java / .NET : the import of modules is not standard in JavaScript until ECMAScript 6.