A model for reasoning about JavaScript promises

Abstract

In JavaScript programs, asynchrony arises in situations such as web-based user-interfaces, communicating with servers through HTTP requests, and non-blocking I/O. Event-based programming is the most popular approach for managing asynchrony, but suffers from problems such as lost events and event races, and results in code that is hard to understand and debug. Recently, ECMAScript 6 has added support for promises, an alternative mechanism for managing asynchrony that enables programmers to chain asynchronous computations while supporting proper error handling. However, promises are complex and error-prone in their own right, so programmers would benefit from techniques that can reason about the correctness of promise-based code.Since the ECMAScript 6 specification is informal and intended for implementers of JavaScript engines, it does not provide a suitable basis for formal reasoning. This paper presents λ p , a core calculus that captures the essence of ECMAScript 6 promises. Based on λ p , we introduce the promise graph, a program representation that can assist programmers with debugging of promise-based code. We then report on a case study in which we investigate how the promise graph can be helpful for debugging errors related to promises in code fragments posted to the StackOverflow website.

Finding broken promises in asynchronous JavaScript programs

“…As a result, developers often make mistakes while creating, settling, linking, and synchronizing various promise objects. As such, common error-prone patterns manifest in promise-based JavaScript applications [Madsen et al 2017]. We use three examples, presented in Figures 1ś6, to illustrate the challenging nature of understanding and debugging promise-based code.…”

“…In this section, we define the notion of a promise graph. Our definition is based on the original definition of a promise graph by Madsen et al [Madsen et al 2017], but a key difference is that our promise graphs are computed using dynamic analysis, whereas the definition by Madsen et al is assumed to be computed using static analysis 11 . To emphasize this distinction, we will henceforth use the term static promise graphs to refer to the static notion proposed by Madsen et al, and dynamic promise graphs to refer to the dynamic notion used in the present paper.…”

“…• We extend the promise graph proposed by Madsen et al [2017] to handle all aspects ECMA-Script 6 promises, including default reactions, exceptions, and the synchronization operations all and race. • We implement a dynamic analysis in an open-source tool called PromiseKeeper to automatically construct the promise graph for a specific execution [PromiseKeeper 2018].…”

“…Next, in Section 3 we use three examples taken from GitHub to illustrate the problems that can arise in promise-based code. Section 4 defines the promise graph, as an extension of the promise graphs of Madsen et al [2017]. Section 5 discusses how the promise graph can be used to aid debugging by detecting occurrences of several anti-patterns.…”

A Survey of Asynchronous Programming Using Coroutines in the Internet of Things and Embedded Systems

“…A solution to the split-phase problem for desktop so ware has been language support for coroutines (Conway 1963;Knuth 1997;Marlin 1979) and promises (Brodu et al 2015;Liskov and Shrira 1988;Madsen et al 2017). For example, in C#, JavaScript, and Python, developers can use an "await" keyword to wait on an external event.…”