Layered JavaScript engines, in which the JavaScript runtime is built on top another managed runtime, provide better extensibility and portability compared to traditional monolithic engines. In this paper, we revisit the design of layered JavaScript engines and propose a layered architecture, called MuscalietJS2, that splits the responsibilities of a JavaScript engine between a high-level, JavaScript-specific component and a low-level, language-agnostic .NET VM. To make up for the performance loss due to layering, we propose a two pronged approach: high-level JavaScript optimizations and exploitation of low-level VM features that produce very efficient code for hot functions. We demonstrate the validity of the MuscalietJS design through a comprehensive evaluation using both the Sunspider benchmarks and a set of web workloads. We demonstrate that our approach outperforms other layered engines such as IronJS and Rhino engines while providing extensibility, adaptability and portability.

We explore the challenges in expressing and managing concurrency in browsers on mobile devices. Browsers are complex applications that implement multiple standards, need to support legacy behavior, and are highly dynamic and interactive. We present ZOOMM, a highly concurrent web browser engine prototype and show how concurrency is effectively exploited at different levels: speed up computation performance, preload network resources, and preprocess resources outside the critical path of page loading. On a dual-core Android mobile device we demonstrate that ZOOMM is two times faster than the native WebKit based browser when loading the set of pages defined in the Vellamo benchmark.