Inference and Evolution of TypeScript Declaration Files

Abstract

Abstract. TypeScript is a typed extension of JavaScript that has become widely used. More than 2 000 JavaScript libraries now have publicly available TypeScript declaration files, which allows the libraries to be used when programming TypeScript applications. Such declaration files are written manually, however, and they are often lagging behind the continuous development of the libraries, thereby hindering their usability. The existing tool tscheck is capable of detecting mismatches between the libraries and their declaration files, but it is less suitable when creating and evolving declaration files. In this work we present the tools tsinfer and tsevolve that are designed to assist the construction of new TypeScript declaration files and support the co-evolution of the declaration files as the underlying JavaScript libraries evolve. Our experimental results involving major libraries demonstrate that tsinfer and tsevolve are superior to tscheck regarding these tasks and that the tools are sufficiently fast and precise for practical use.

Type test scripts for TypeScript testing

“…Mismatches were found in 49 of the 54 benchmarks, independently of the timeout and the number of repeated runs. This confirms the results from Feldthaus and Mùller [2014], Kristensen and Mùller [2017], and Williams et al [2017] that errors are common, even in declaration files for highly popular libraries. The numbers in Table 1 are quite large, and there are likely not around 6 000 unique errors among the 54 libraries tested.…”

“…In this work we present a new method for detecting mismatches between JavaScript libraries and their TypeScript declaration files. Compared to the approaches by Feldthaus and Mùller [2014] and Kristensen and Mùller [2017] that rely on static analysis, our method finds more actual errors and also reports fewer false positives. It additionally has the advantage that each reported mismatch is witnessed by a concrete execution, which aids diagnosis and debugging.…”

“…JavaScript implementations evolve [Kristensen and Mùller 2017]. However, those techniques rely on unsound static analysis and consequently often overlook errors and report spurious warnings.…”

“…Thus, any additional errors arising from calling these method will remain undetected until the first mismatch is fixed. Some mismatches are introduced intentionally by the programmer, for example to circumvent limitations in the expressiveness of TypeScript's type system, as observed in previous work [Feldthaus and Mùller 2014;Kristensen and Mùller 2017], so it is important that we do not stop testing at the first mismatch we find and require the programmer to fix that mismatch before proceeding. For this reason, we let assertType perform the deep type check on all the reachable objects and report a mismatch if the check fails, but the decision whether the value shall be stored for feedback testing is based on a shallow check.…”

“…We evaluate three main aspects of the approach, each with some sub-questions: 1) Quantitative evaluation How many type mismatches does TStest find in real-world TypeScript declarations for JavaScript libraries, and how much time is needed to run the analysis? Furthermore, how do the different design choices discussed in As benchmarks for experiments we use all of the libraries used by Feldthaus and Mùller [2014] and Kristensen and Mùller [2017], and 32 other randomly selected popular JavaScript libraries. 19 We exclude libraries that write to the local file system.…”