Toward automatic update from callbacks to promises

Javascript is the prevalent scripting language for the web. It lets web pages register callbacks to react to user events. A callback is a function to be invoked later with a result currently unavailable. This pattern also proved to respond efficiently to remote requests. Javascript is currently used to implement complete web applications. However, callbacks are ill-suited to arrange a large asynchronous execution flow. Promises are a more adapted alternative. They provide a unified control over both the synchronous and asynchronous execution flows. The next version of Javascript proposes to replace callbacks with Promises. This paper brings the first step toward a compiler to help developers prepare this shift. We present an equivalence between callbacks and Dues. The latter are a simpler specification of Promises developed for the purpose of this demonstration. From this equivalence, we implement a compiler to transform an imbrication of callbacks into a chain of Dues. This equivalence is limited to Node.js-style asynchronous callbacks declared in situ. We evaluate our compiler over 64 npm packages, 9 of them present compatible callbacks and compile successfully. We consider this shift to be a first step toward the merge of concepts from the data-flow programming model into the imperative programming model.