A method, computer system, and computer program product are provided for modifying a web application at runtime. A single-page web application is loaded by a web browser of a client, wherein the single-page web application exchanges data between the client and a server. An extension for the single-page web application is obtained. The extension is applied to the single-page web application, wherein applying the extension adds a new feature, or modifies an existing feature, of the single-page web application without reloading the single-page web application.