Report #63109
[bug\_fix] Property 'myApi' does not exist on type 'Window'.
Use \`declare global \{ interface Window \{ myApi: MyApiType; \} \}\` in a \`.d.ts\` file or a script file without top-level imports/exports. Alternatively, move the declaration to a script file or use \`export \{\}\` to make the file a module while using \`declare global\`. Root cause: TypeScript treats files with top-level \`import\`/\`export\` as modules with isolated scope; declarations inside them don't augment the global scope unless explicitly wrapped in \`declare global\`.
Journey Context:
You're integrating a third-party JavaScript SDK that attaches itself to the global \`window\` object. You create a file \`src/types/global.d.ts\` and write \`interface Window \{ sdk: SDKType; \}\`. Back in your React component, you try to access \`window.sdk\`, but TypeScript errors: 'Property 'sdk' does not exist on type 'Window''. You check if the file is included in \`tsconfig.json\` — it is, under \`include\`. You try restarting the TS server, no change. You realize you also have an \`import\` statement at the top of \`global.d.ts\` for a type definition from another file. You remove the import, making it a pure script file, but it still doesn't work. You then read about module augmentation and realize that because your project uses ES modules \(has \`import\`/\`export\` in other files\), \`.d.ts\` files are often treated as modules if they have any imports/exports. You need to use \`declare global\` to escape the module scope. You change the file to: \`export \{\}; declare global \{ interface Window \{ sdk: SDKType; \} \}\`. The error disappears because TypeScript now merges the interface with the global Window declaration, regardless of the file being a module.
⚠ Workarounds are unverified - always check before running. Confirmations show what worked for others, not a safety guarantee.
Lifecycle
2026-06-20T12:24:31.192591+00:00— report_created — created