Thread-Level Speculation can be used to take advantage of multicore architectures for web applications. We have implemented Thread-Level Speculation in the state-of-the-art JavaScript engine V8 instead of using an interpreted JavaScript engine. We evaluate the implementation with the Chromium web browser on 15 popular web applications for 2, 4, and 8 cores. The results show that it is benecial to combine Thread-Level Speculation and Just-in-time compi-lation and that it is possible to take advantage of multicore architectures while hiding the details of parallel program-ming from the programmer of web applications.