--- title: How to fix `undefined is not an object (evaluating... description: Safari throws this error when JavaScript tries to access `window.webkit.messageHandlers`, which only exists inside WKWebView when native iOS/macOS apps... canonical: https://daily.dev/posts/918fdbkt4 twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: How to fix `undefined is not an object (evaluating 'window.webkit.messageHandlers')` | daily.dev og:description: Safari throws this error when JavaScript tries to access `window.webkit.messageHandlers`, which only exists inside WKWebView when native iOS/macOS apps... og:url: https://daily.dev/posts/918fdbkt4 og:image: https://api.daily.dev/og/posts/918FDBkt4.png og:image:alt: Post cover image 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. # How to fix `undefined is not an object (evaluating 'window.webkit.messageHandlers')` **[All Frontend](https://daily.dev/sources/allfrontend)** · [@toddhgardner](https://daily.dev/toddhgardner) · 0 upvotes · 0 comments ## Summary Safari throws this error when JavaScript tries to access `window.webkit.messageHandlers`, which only exists inside WKWebView when native iOS/macOS apps register a handler. The issue typically occurs when WKWebView-specific code runs in a normal browser context. Fix it by wrapping calls with feature detection using optional chaining or explicit checks before accessing the bridge. If you control the native app, verify the handler is registered correctly with the exact name before JavaScript executes. Monitor production errors to determine if this affects real users or is harmless noise from unsupported contexts. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Similar posts on daily.dev - [Catch JavaScript errors with user-friendly error feedback](https://daily.dev/posts/catch-javascript-errors-with-user-friendly-error-feedback-ecje7ol0s) · RUBYLAND · 0 upvotes · 0 comments - [Fixing Top-Level Await in Safari](https://daily.dev/posts/fixing-top-level-await-in-safari-kcsplb3aq) · WebKit · 14 upvotes · 3 comments - [Browsers Treat Big Sites Differently](https://daily.dev/posts/browsers-treat-big-sites-differently-hldbesd4b) · Lobsters · 8 upvotes · 1 comments - [WebKit supports interactive-widget … and hopefully Safari will too?](https://daily.dev/posts/webkit-supports-interactive-widget-and-hopefully-safari-will-too--hig21dyrd) · Bram.us · 9 upvotes · 3 comments --- Tags: [#javascript](https://daily.dev/tags/javascript), [#ios](https://daily.dev/tags/ios), [#safari](https://daily.dev/tags/safari) [View this post on daily.dev](https://daily.dev/posts/918fdbkt4) ```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/918fdbkt4","headline":"How to fix `undefined is not an object (evaluating 'window.webkit.messageHandlers')`","text":"Shared: How to fix `undefined is not an object (evaluating 'window.webkit.messageHandlers')`","url":"https://daily.dev/posts/918fdbkt4","datePublished":"2026-02-04T05:00:53.497Z","dateModified":"2026-02-04T05:00:53.501Z","author":{"@type":"Person","name":"Todd Gardner","url":"https://daily.dev/toddhgardner","image":"https://media.daily.dev/image/upload/s--0uADve-Y--/f_auto/v1760631400/avatars/avatar_98cai8UH2NmelWmHe6IdN?_a=BAMAK+ZW0","description":"I start things.","interactionStatistic":{"@type":"InteractionCounter","interactionType":{"@type":"EndorseAction"},"userInteractionCount":150}},"image":"https://media.daily.dev/image/upload/s--ZrL_HSsR--/f_auto/v1722860399/public/Placeholder%2006","interactionStatistic":[{"@type":"InteractionCounter","interactionType":{"@type":"LikeAction"},"userInteractionCount":0},{"@type":"InteractionCounter","interactionType":{"@type":"CommentAction"},"userInteractionCount":0}],"sharedContent":{"@type":"WebPage","url":"https://api.daily.dev/r/OGy9CepAJ"},"isPartOf":{"@type":"WebPage","url":"https://daily.dev/squads/allfrontend","name":"All Frontend"}} {"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https://daily.dev"},{"@type":"ListItem","position":2,"name":"All Frontend","item":"https://daily.dev/squads/allfrontend"},{"@type":"ListItem","position":3,"name":"How to fix `undefined is not an object (evaluating 'window.webkit.messageHandlers')`"}]} ```