--- title: Treat boundary data as unknown. | daily.dev description: A short guide argues that data crossing a boundary (like an API response) should be treated as unknown rather than trusted via type assertions. It recommends... canonical: https://daily.dev/posts/treat-boundary-data-as-unknown--rue3fw988 twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Treat boundary data as unknown. | daily.dev og:description: A short guide argues that data crossing a boundary (like an API response) should be treated as unknown rather than trusted via type assertions. It recommends... og:url: https://daily.dev/posts/treat-boundary-data-as-unknown--rue3fw988 og:image: https://api.daily.dev/og/posts/rue3fW988.png og:image:alt: Treat boundary data as unknown. 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. # Treat boundary data as unknown. **[nyaomaru](https://daily.dev/sources/graxwfjk0eop4zs3tdzdr)** · [@nyaomaru](https://daily.dev/nyaomaru) · 1 min read · 0 upvotes · 0 comments ## Summary A short guide argues that data crossing a boundary (like an API response) should be treated as unknown rather than trusted via type assertions. It recommends validating with composable guard functions and using a safeParse-style approach to narrow the type only after runtime verification, avoiding the false safety of TypeScript type assertions. ## Content Validate it with composable guards, then let `safeParse` narrow the result. A type assertion performs no runtime check. [https://is-kit.dev/guides/validate-unknown-without-schema-library](https://is-kit.dev/guides/validate-unknown-without-schema-library) #typescript #opensource #cleancode ## Similar posts on daily.dev - [How to Defend Your JavaScript App Against Unsafe Data with TypeScript Guard Utilities](https://daily.dev/posts/how-to-defend-your-javascript-app-against-unsafe-data-with-typescript-guard-utilities-cuooqjnij) · freeCodeCamp · 5 upvotes · 1 comments - [Stop drifting around in the dark when using "any" and "unknown" TypeScript types](https://daily.dev/posts/stop-drifting-around-in-the-dark-when-using-any-and-unknown-typescript-types-89bkfo9pv) · This is Learning · 0 upvotes · 0 comments - [Parse, Don't Validate — In a Language That Doesn't Want You To](https://daily.dev/posts/parse-don-t-validate-in-a-language-that-doesn-t-want-you-to-zyfa03chk) · Lobsters · 0 upvotes · 0 comments --- Tags: [#open-source](https://daily.dev/tags/open-source), [#typescript](https://daily.dev/tags/typescript), [#appsec](https://daily.dev/tags/appsec) [View this post on daily.dev](https://daily.dev/posts/treat-boundary-data-as-unknown--rue3fw988) ```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":"DiscussionForumPosting","mainEntityOfPage":"https://daily.dev/posts/treat-boundary-data-as-unknown--rue3fw988","headline":"Treat boundary data as unknown.","text":"A short guide argues that data crossing a boundary (like an API response) should be treated as unknown rather than trusted via type assertions. 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