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TypeScript 3.5 RC Fixes Introduced Bug that Caused Slowness 'Explosion'

Microsoft shipped TypeScript 3.5 RC, a release candidate that fixes a type-checking bug the dev team introduced in version 3.4, which caused a huge slowdown in build times and other performance.

"Unfortunately, as part of a bug fix in TypeScript 3.4 we accidentally introduced a regression that could lead to an explosion in how much work the type-checker did, and in turn, type-checking time," said Daniel Rosenwasser, program manager, in a blog post yesterday (May 16). "The most-impacted set of users were those using the styled-components library. This regression was serious not just because it led to much higher build times for TypeScript code, but because editor operations for both TypeScript and JavaScript users became unbearably slow."

In the new TypeScript 3.5 RC, affected operations are now even faster than they were in v3.3.

Coincidentally, the fix addressing the "explosion" in type-checking work came shortly after analyst firm RedMonk announced an explosion in the popularity of the open source programming language, gaining new heights of adoption due to its introduction of optional static typing, which is lacking in parent JavaScript (see Development Analyst: 'TypeScript Is Exploding').

In addition to the bug fix and other speed improvements, Rosenwasser summed up other 3.5 changes thusly:

As the final TypeScript 3.5 is expected to ship at the end of this month, developers have a short time to put the RC through its paces and provide feedback to the dev team. Rosenwasser previously indicated developers can report problems by filing an issue on GitHub.

As for future plans, he pointed to the TypeScript 3.5 Iteration Plan and the roadmap.

About the Author

David Ramel is the editor of Visual Studio Magazine.

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