How is Dynatrace capturing api calls timings from a browser?

[adtuser]

Inspecting (in Chrome) all the API calls from our web app, it looks like the ruxitagentjs is initiating all the api calls to our backend. Does Dynatrace track RUM waterfall data by injected and proxying all outbound requests? 
Thank you

[AntonioSousa]

Dynatrace uses a standard API that browsers make available. All timing information is gathered by the browser, and it is from the browser that Dynatrace gets the data...

[adtuser]

Thank you. But why do we see the ruxitagentjs initiating all the requests to our backend?