MapLibre GL JS v5 → v6 Migration

MapLibre GL JS v6 (released 2026-07-22) removed several things v5 code relied on: the UMD/CSP browser bundles, the default export, CommonJS support, the internal map.transform, and the MapDataEvent type. Most models' training data predates v6. So the natural-sounding answer to "how do I do X" is usually the v5 answer, and it breaks on v6.

Primary reference: the MapLibre GL JS v5→v6 migration guide. This skill adds the gaps a model tends to fill with v5-era defaults. If the guide and this skill disagree, follow the guide and report it.

When to Use This Skill

• Upgrading an existing MapLibre GL JS v5 app to v6, or debugging a map that "used to work" after a dependency update
• Writing one of the seven patterns below: a CDN <script> tag, an import statement, a require() call, a styleimagemissing handler, code that reads map.transform, a typed data/dataloading/dataabort handler, or a bundler setup (Vite, webpack, esbuild, Rspack, Rollup)
• Debugging errors like ERR_PACKAGE_PATH_NOT_EXPORTED, a blank map after a CDN update, a sprite icon that never appears, a TypeScript error naming MapDataEvent, or a worker-loading error that blocks render

Don't use this skill to pad an unrelated answer. It covers seven narrow breaking changes, not general v6 best practice. A question about sources, layers, styling, or terrain gets a normal, focused answer with no migration reminders attached.

1. CDN script tag: ESM-only now

v6 removed the UMD bundle and the separate CSP build. There's no dist/maplibre-gl.js for a plain <script src="..."> tag anymore. Only the ESM build, dist/maplibre-gl.mjs, remains, and it needs type="module".