--- title: Parse, Don't Guess | daily.dev description: A developer shares how a sneaky Regex-based bigint auto-detection during JSON deserialization caused JavaScript event loop freezes in production. The fix... canonical: https://daily.dev/posts/parse-don-t-guess-cu2bmxcqr twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Parse, Don't Guess | daily.dev og:description: A developer shares how a sneaky Regex-based bigint auto-detection during JSON deserialization caused JavaScript event loop freezes in production. The fix... og:url: https://daily.dev/posts/parse-don-t-guess-cu2bmxcqr og:image: https://api.daily.dev/og/posts/cU2BmxCQR.png og:image:alt: Parse, Don't Guess og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # Parse, Don't Guess **[Architecture Weekly](https://daily.dev/sources/architectureweekly)** · 16 min read · 86 upvotes · 1 comments ## Summary A developer shares how a sneaky Regex-based bigint auto-detection during JSON deserialization caused JavaScript event loop freezes in production. The fix involved dropping the global Regex reviver and replacing it with an explicit upcasting pattern — a function that converts stored types (strings) to application types (Date, bigint) only for declared fields. This same upcasting mechanism naturally extends to schema versioning: handling structural changes between document/event versions (V1 flat fields vs V2 nested objects) using upcast (read) and downcast (write) functions. The pattern is applied to both Pongo (document store) and Emmett (event store), enabling backward and forward compatibility without batch migrations. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Community discussion Top comments from developers on daily.dev. **@pboling** · 0 upvotes > If you are interested in this sort of thing for Ruby (real AST/PEG parsing instead of Regex guessing): https://github.com/kettle-rb/tree_haver --- Tags: [#architecture](https://daily.dev/tags/architecture), [#typescript](https://daily.dev/tags/typescript) [View this post on daily.dev](https://daily.dev/posts/parse-don-t-guess-cu2bmxcqr) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"Parse, Don't Guess","url":"https://daily.dev/posts/parse-don-t-guess-cu2bmxcqr","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/parse-don-t-guess-cu2bmxcqr"},"datePublished":"2026-03-02T17:24:04.172Z","dateModified":"2026-03-02T17:24:36.160Z","description":"A developer shares how a sneaky Regex-based bigint auto-detection during JSON deserialization caused JavaScript event loop freezes in production. 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