ozan•2mo ago

ERR_UNSUPPORTED_ESM_URL_SCHEME when building an Astro app with React islands

After deno task astro add react , deno task build fails with ERR_UNSUPPORTED_ESM_URL_SCHEME. All the information online points to using node or bun. I'm not entirely familiar with details of build systems. So I need help! 🙂 My deno.json looks like this:

{
  "imports": {
    "@astrojs/alpinejs": "npm:@astrojs/alpinejs@^0.4.9",
    "@astrojs/react": "npm:@astrojs/react@^4.4.0",
    "@deno/astro-adapter": "npm:@deno/astro-adapter@^0.3.1",
    "@tailwindcss/typography": "npm:@tailwindcss/typography@^0.5.16",
    "@tailwindcss/vite": "npm:@tailwindcss/vite@^4.1.13",
    "@types/alpinejs": "npm:@types/alpinejs@^3.13.11",
    "@types/react": "npm:@types/react@^19.1.13",
    "@types/react-dom": "npm:@types/react-dom@^19.1.9",
    "alpinejs": "npm:alpinejs@^3.15.0",
    "astro": "npm:astro@^5.13.7",
    "clsx": "npm:clsx@^2.1.1",
    "prettier": "npm:prettier@^3.6.2",
    "prettier-plugin-astro": "npm:prettier-plugin-astro@^0.14.1",
    "react": "npm:react@^19.1.1",
    "react-dom": "npm:react-dom@^19.1.1",
    "tailwindcss": "npm:tailwindcss@^4.1.13"
  },
  "tasks": {
    "dev": "deno run -A npm:astro dev",
    "build": "deno run -A npm:astro build",
    "preview": "deno run -A npm:astro preview",
    "astro": "deno run -A npm:astro"
  },
  "nodeModulesDir": "auto"
}

{
  "imports": {
    "@astrojs/alpinejs": "npm:@astrojs/alpinejs@^0.4.9",
    "@astrojs/react": "npm:@astrojs/react@^4.4.0",
    "@deno/astro-adapter": "npm:@deno/astro-adapter@^0.3.1",
    "@tailwindcss/typography": "npm:@tailwindcss/typography@^0.5.16",
    "@tailwindcss/vite": "npm:@tailwindcss/vite@^4.1.13",
    "@types/alpinejs": "npm:@types/alpinejs@^3.13.11",
    "@types/react": "npm:@types/react@^19.1.13",
    "@types/react-dom": "npm:@types/react-dom@^19.1.9",
    "alpinejs": "npm:alpinejs@^3.15.0",
    "astro": "npm:astro@^5.13.7",
    "clsx": "npm:clsx@^2.1.1",
    "prettier": "npm:prettier@^3.6.2",
    "prettier-plugin-astro": "npm:prettier-plugin-astro@^0.14.1",
    "react": "npm:react@^19.1.1",
    "react-dom": "npm:react-dom@^19.1.1",
    "tailwindcss": "npm:tailwindcss@^4.1.13"
  },
  "tasks": {
    "dev": "deno run -A npm:astro dev",
    "build": "deno run -A npm:astro build",
    "preview": "deno run -A npm:astro preview",
    "astro": "deno run -A npm:astro"
  },
  "nodeModulesDir": "auto"
}

2 Replies

bartlomieju•2mo ago

The problem is most likely that Astro doesn't understand demo.json file - it will most likely work if you move over to package.json file

ozanOP•2mo ago

This was helpful, thanks!

ERR_UNSUPPORTED_ESM_URL_SCHEME when building an Astro app with React islands

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