Remedying the Eval that Men Do

Simon Holm Jensen, Peter A. Jonsson, and Anders Møller


A range of static analysis tools and techniques have been developed in recent years with the aim of helping JavaScript web application programmers produce code that is more robust, safe, and efficient. However, as shown in a previous large-scale study, many web applications use the JavaScript eval function to dynamically construct code from text strings in ways that obstruct existing static analyses. As a consequence, the analyses either fail to reason about the web applications or produce unsound or useless results.

We present an approach to soundly and automatically transform many common uses of eval into other language constructs to enable sound static analysis of web applications. By eliminating calls to eval, we expand the applicability of static analysis for JavaScript web applications in general.

The transformation we propose works by incorporating a refactoring technique into a dataflow analyzer. We report on our experimental results with a small collection of programming patterns extracted from popular web sites. Although there are inevitably cases where the transformation must give up, our technique succeeds in eliminating many nontrivial occurrences of eval.

(ACM SIGSOFT Distinguished Paper)

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