The current event-based model of web client programming lacks of a high level abstraction for concurrency and communication when many interactions are involved. The design of JavaScript runtime in the browser is very simple and chains steps of input handling and computation of output in a sequential way. This definition describes exactly a subset of programs well handled by the synchronous-reactive model. It proposes constructs to express parallel tasks communicating through broadcasted signals enforcing a static hypothesis of determinism, coherency and causality that improve programs composition. It is then interesting to consider client events as inputs and web view elements as outputs of a synchronous-reactive program. We describe here the design of pendulum, a language extension implementing those principles and targeting web client programming, which generates fast sequential code.