This paper presents a JavaScript Foreign Function Interface for a Scheme implementation hosted on JavaScript and supporting threads. In order to be as convenient as possible the foreign code is expressed using infix syntax, the type conversions between Scheme and JavaScript are mostly implicit, and calls can both be done from Scheme to JavaScript and the other way around. Our approach takes advantage of JavaScript’s dynamic nature and its support for asynchronous functions. This allows concurrent activities to be expressed in a direct style in Scheme using threads. The paper goes over the design and implementation of our approach in the Gambit Scheme system. Examples are given to illustrate its use.