Mining Rule Violations in JavaScript Code Snippets

Programming code snippets readily available on platforms such as StackOverflow are undoubtedly useful for software engineers. Unfortunately, these code snippets might contain issues such as deprecated, misused, or even buggy code. These issues could pass unattended, if developers do not have adequate knowledge, time, or tool support to catch them. In this work we expand the understanding of such issues (or the so called "violations") hidden in code snippets written in JavaScript, the programming language with the highest number of questions on StackOverflow. To characterize the violations, we extracted 336k code snippets from answers to JavaScript questions on StackOverflow and statically analyzed them using ESLinter, a JavaScript linter. We discovered that there is no single JavaScript code snippet without a rule violation. On average, our studied code snippets have 11 violations, but we found instances of more than 200 violations. In particular, rules related to stylistic issues are by far the most violated ones (82.9% of the violations pertain to this category). Possible errors, which developers might be more interested in, represent only 0.1% of the violations. Finally, we found a small fraction of code snippets flagged with possible errors being reused on actual GitHub software projects. Indeed, one single code snippet with possible errors was reused 1,261 times.