VCR: Record ajax request to later playback


Record XMLHttpRequest calls and saves them using localStorage or files if using Nodejs. It's a js implementation of myronmarston's VCR but for javasccript without any dependencies

$ npm install vcr
VCR.configure(function(c) {
  c.hookInto = window.XMLHttpRequest;
  c.cassetteLibraryDir = "recorder"; // default: 'cassettes' = "http://localhost:9393/"; // will prepend req url 

The only required config it's wich object to intercept, for now only works with XMLHttpRequest to catch ajax requests.

hookInto: object to intercept cassetteLibraryDir: when using nodejs defines where to store cassettes host: usefull when running within node and want to cache request to save, destroy, update, etc.

I try to make it as similar to original VCR as possible. Using Gerbil it's something like this:

scenario("Ajax interception", {
  'setup'function() {
    VCR.configure(function(c) {
      c.hookInto = window.XMLHttpRequest;
  'Recording ajax request'function(g) {
    VCR.useCassette('test', function(v) {
      XMLHttpRequest = v.XMLHttpRequest;
      var makeRequest = function() {
        var ajax = new XMLHttpRequest();
'GET', 'test.html');
        ajax.onreadystatechange = function() {
          if(ajax.readyState === 4) {
            g.assertEqual("Hello World!\n", ajax.responseText);
      // Record First Request 
      // Wait for it... 
      g.setTimeout(function() { makeRequest(); }, 100);

If you are using nodejs .json files will be created as cassetes to reproduce afterwards. In the other hand if you are running it in a browser localStorage will be used to persist the recordings.

Pablo Dejuan for the idea.