appsmithorg/appsmith · error · ImportError

The script at ${url} cannot be installed.

Error message

The script at ${url} cannot be installed.

What it means

Thrown as ImportError(url) inside installLibrary (the singular/classic install path) when both fallbacks fail: self.importScripts(url) threw, and the subsequent dynamic import(/* webpackIgnore: true */ url) also threw. The library URL could be loaded neither as a classic script nor as an ES module, so it is reported as uninstallable. The message is 'The script at ${url} cannot be installed.'

Source

Thrown at app/client/src/workers/Evaluation/handlers/jsLibrary.ts:216

      log.debug(e, `importScripts failed for ${url}`);
      try {
        // If importScripts fails, try to import the library using dynamic import
        module = await import(/* webpackIgnore: true */ url);

        // If the module is not an object, it is not a valid ESM library
        if (module && typeof module === "object") {
          const uniqAccessor = generateUniqueAccessor(
            url,
            takenAccessors,
            takenNamesMap,
          );

          self[uniqAccessor] = flattenModule(module);
          accessors.push(uniqAccessor);
        }
      } catch (e) {
        log.debug(e, `dynamic import failed for ${url}`);
        throw new ImportError(url);
      }
    }

    // If no accessors at this point, installation likely failed.
    if (accessors.length === 0) {
      throw new Error("Unable to determine a unique accessor");
    }

    // Name of the library is the last accessor. This is totally random and needs fixing.
    const name = accessors[accessors.length - 1];

    defs["!name"] = `LIB/${name}`;
    try {
      for (const key of accessors) {
        defs[key] = makeTernDefs(self[key]);
      }
    } catch (e) {
      for (const acc of accessors) {

View on GitHub (pinned to 8cd9021c24)

Solutions

1. Open the URL in a browser/incognito and confirm it returns raw JavaScript (not HTML) with HTTP 200.
2. Switch to a reliable CDN form, e.g. the jsDelivr ESM URL https://cdn.jsdelivr.net/npm/<pkg>@<version>/+esm, or a UMD build for importScripts.
3. Verify the host permits cross-origin script loading (CORS / Access-Control-Allow-Origin: *).
4. Check network/proxy/DNS from the Appsmith server/pod; the fetch happens in the evaluation worker.
5. Try a pinned version (@x.y.z) instead of @latest to avoid a deleted/renamed tag.

Example fix

// before (importable URL invalid)
https://example.com/lib.min.js  // returns HTML 404 page

// after
https://cdn.jsdelivr.net/npm/lodash@4.17.21/lodash.min.js

// Validate a URL before handing it to the library installer
function isValidLibUrl(raw) {
  let u;
  try { u = new URL(raw); } catch { return false; }
  if (u.protocol !== 'https:' && u.protocol !== 'http:') return false;
  return /\.(js|mjs)$/i.test(u.pathname) || u.pathname.includes('+esm');
}
// usage: only install when isValidLibUrl(url) is true

const isInstallableUrl = (raw) => {
  try {
    const u = new URL(raw, location.href);
    return (u.protocol === 'https:' || u.protocol === 'http:')
      && /\.(js|mjs)$/i.test(u.pathname);
  } catch { return false; }
};

// The installer surfaces this as a failed install result; handle it in the UI:
try {
  await installLibrary(url);
} catch (e) {
  if (e?.name === 'ImportError') {
    showToast(`Could not install ${url}. Check the URL, CORS, and network.`);
  } else throw e;
}

When it happens

Trigger: Adding an external JS library URL in the Appsmith library installer that 404s, is not valid JavaScript, is blocked by CORS for both importScripts and dynamic import, returns HTML (e.g. a CDN error page), or is a non-module file that importScripts cannot parse. Network offline / DNS failure during install also lands here.

Common situations: Using a raw GitHub URL instead of a CDN URL; pointing at a /src/ file rather than a built bundle; CDN returns a 5xx; corporate proxy blocks the host; the URL serves ESM-only content but the worker's importScripts path fails and the dynamic-import fallback also errors.

Related errors

• Unable to determine a unique accessor
• Failed to generate autocomplete definitions for ${name}.
• Unable to generate a unique accessor
• Failed to load JS libraries
• ${extractExecutionErrorMessage(e)}

AI-assisted analysis of appsmithorg/appsmith@8cd9021c24 (2026-08-12). Data as JSON: /api/errors/32868f9949539756. Report an issue: GitHub.