Cleanroom: Edit-Time Error Detection with the Uniqueness Heuristic

Many dynamic programming language features, such as implicit declaration, reflection, and code generation, make it difficult to verify the existence of identifiers through standard program analysis. We present an alternative verification, which, rather than analyzing the semantics of code, highlights any name or pair of names that appear only once across a program’s source files. This uniqueness heuristic is implemented for HTML, CSS, and JavaScript, in an interactive editor called Cleanroom, which highlights lone identifiers after each keystroke. Through an online experiment, we show that Cleanroom detects real errors, that it helps developers find these errors more quickly than developers can find them on their own, and that this helps developers avoid costly debugging effort by reducing how many times a program is executed with potential errors. The simplicity and power of Cleanroom’s heuristic may generalize well to other dynamic languages with little support for edit-time name verification.