Toward automatic update from callbacks to promises

Abstract

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.

Finding broken promises in asynchronous JavaScript programs

“…Kambona et al [2013] report on a case study that investigates the effectiveness of promises and reactive extensions using an example of an online collaborative drawing editor. Brodu et al [2015] propose a technique to automatically refactoring legacy JavaScript code, written using event-handling and callbacks, into promise-based code. Gallaba et al [2017] present an empirical study in which they report on the prevalence of callback-accepting functions and callsites, and discuss several solutions for rewriting callbackbased code using alternative mechanisms for accommodating asynchrony, including Async.js and promises.…”

Refactoring Asynchrony in JavaScript

“…The closest prior work is by Brodu et al [12] who propose a compiler for converting nested callbacks into a sequence of Dues, which is a simpler version of promises. There are several drawbacks to this approach: (1) the source code does not change, so it does not eliminate the issues with understandability, (2) Dues do not support the critical notions of rejection and resolution in promises and can therefore only re-write the error-first protocol in a simplified notation, (3) their approach requires developers to manually specify asynchronous callbacks that are suitable candidates to be converted.…”

Transforming JavaScript event-loop into a pipeline

“…This application, simplified in listing 3, is a real-time chat using gif-based communication channels. It was selected in a previous work [5] from the npm registry because it depends on express, it is tested, working, and simple enough to illustrate this evaluation. The server transforms the received text into a gif frame, and pushes it back to a never-ending gif to be displayed on the client.…”