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Rollup watch mode: library bundles, CORS on demo HTML pages, and UMD versus IIFE globals
When you ship UMD builds consumed from third-party sites, your API must emit explicit CORS because the script origin differs from your API host.
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rolluplibrarycors
External dependencies
Mark peer dependencies as external in Rollup to avoid duplicating fetch polyfills that alter CORS behavior.
Dual ESM/CJS outputs should share the same API base URL resolution logic.
Source maps
Publish maps to a CDN with CORS enabled for browsers to unminify stack traces in consumer SPAs.
Private npm registries may wrap tarball URLs—verify Allow-Origin on those asset hosts too.