Instrumentation platforms facilitate the development and deployment of dynamic analyses. The state-of-the-art instrumentation platforms for JavaScript rely on different weaving approaches for instrumentation, offering different levels of analysis expressiveness. The main issue is that they are unable to observe and reason about abstract operations as these operations are not exposed to language constructs. However, abstract operations are pivotal to understanding JavaScript’s runtime behaviour. This paper demonstrates the importance of exposing the ToPrimitive abstract operation, which lies at the core of JavaScript’s type coercion. We introduce BoaSpect, an interpreter-based instrumentation platform for JavaScript, which provides increased expressiveness by exposing the ToPrimitive trap through the instrumentation interface. We demonstrate its potential by implementing a novel analysis in BoaSpect to identify a potential security exploit, and a taint analysis which can track information flows precisely in the presence of implicit type coercions.