The present invention provides a system and method for real-time communication signaling between HTML5 endpoints and between HTML5 endpoints and the IMS Core of a telecommunication network. In an embodiment the system includes a WebRTC Session Controller (WSC) communicating over an Internet domain protocol with a client-side controller. The client-side controller provides an extensible JavaScript API. The extensible JavaScript API encapsulates the signaling aspect of a communication session of the HTML5 application, including gathering media description, establishing signaling channels, and exchanging media descriptions with the WSC, populating the relevant WebRTC objects, managing the call after it has been established. The extensible JavaScript API which provides for extending the JavaScript API to facilitate development of new types of HTML5 applications without changing the code of the existing JavaScript API.