Based on Fredrickson's (2001) broaden-and-build theory, this study investigates how Foreign Language Enjoyment (FLE; consisting of "teacher appreciation, personal enjoyment," and "social enjoyment") mediates the relationship between Informal Digital Learning of English (IDLE) and EFL secondary students' willingness to communicate in a second language (L2 WTC) inside and outside the classroom. We collected survey data from 308 EFL Hong Kong secondary students who lacked any international experience (ages 12-18). After controlling for demographic data, the results show that teacher appreciation, personal enjoyment, and social enjoyment all mediate the relationship between IDLE and L2 WTC inside the classroom, while personal and social enjoyment mediate the link outside the classroom. A closer look reveals that personal enjoyment, rather than social enjoyment or teacher appreciation, plays a larger role in mediating the relationship. Practically, these findings shed light on the underlying mechanisms by which IDLE and different aspects of FLE can potentially improve the L2 WTC of Asian EFL learners who primarily learn and practice English in the classroom. These findings have implications for future interventions aimed at enhancing L2 WTC by increasing L2 enjoyment in EFL learners.