Small Footprint JavaScript Engine

Abstract

A key programming concept in the world of internet-of-things (IoT) is event-driven computation where events occurred in the ‘things’ are handled by their corresponding event handlers. JavaScript is particularly useful for this computational model due to its properties having event handlers simply programmable. Turning this model into a reality requires a compact, yet powerful JavaScript engine, which can be possibly working on a system equipped with scarce memory and limited CPU of the IoT devices. Although existing JavaScript engines widely being used in web browsers are powerful enough, they require a plenty amount of both static and runtime memory, which cannot fit in the small IoT devices. To handle this space issue, three small footprint JavaScript engines have been proposed previously: Espruino (http://www.espruino.com/), Quad-wheel (https://code.google.com/p/quad-wheel/), and Duktape (http://duktape.org/). This paper compares the three JavaScript engines by evaluating their binary size, runtime memory, and performance, as well as their compatibility of JavaScript tests. It has been found that, out of them, only Duktape correctly supports JavaScript features described in the current standard, yet with mediocre performance and memory requirement. This paper converts Duktape into a better performing one (which we call Duktape+) by applying six optimisations, including efficient property updates and lazy creation of built-in objects. Those optimisations result in as much as 30 % reduction of runtime memory usage and 30 % improvement of performance, with only 2 % increase of its binary size.