how to calculate response times for APIs, in angularJS correctly?

Question

How to calculate response times from AngularJS requests for APIs like get/put/post etc more accurately.

I have intercepted $httpprovider with a timestamp and use that to calculate the responsetimes. (per this)

But when I look at the response times, the response times are incrementing linearly from the browser barring few initial requests. It seems when I compared with browser, it shows a percentage split in firefox (like blocking, ..waittime.. etc). and this whole sum time seems to be increasing linearly but the actual waittime is almost about a mean time.

• 1) How can we get the actual waittime of the response times as accurately as possible as in browser from Javascript? (other than substituting browser with an application?)
• 2) Any idea on if how the browser blocks some requests before getting new requests? does it affect the below code's response time calculations?
• 3) In case of Options pre flight request (currently I can use cache for that) but how does that affect httpprovider calculations ? Does Javascript waits for browser before calling the API or JS calls API and then waits until browser completes preflight/blocking etc?

I am providing the links code here again.

 app.factory('logTimeTaken', [function() {  
    var logTimeTaken = {
        request: function(config) {
            config.requestTimestamp = new Date().getTime();
            return config;
        },
        response: function(response) {
            response.config.responseTimestamp = new Date().getTime();
            return response;
        }
    };
    return logTimeTaken;
}]);
app.config(['$httpProvider', function($httpProvider) {  
    $httpProvider.interceptors.push('logTimeTaken');
}]);

$http.get('url').then(function(response) {
    var time = response.config.responseTimestamp - response.config.requestTimestamp;
    console.log('Time taken ' + (time / 1000) + ' seconds.');
});