What causes "failed to load '{}': {}" in denoland/deno?

Fix the underlying load error for the named specifier (check URL/file availability, run `deno cache --reload`)

failed to load '{}': {}

Error message

failed to load '{}': {}

What it means

During eszip creation, graph.try_get returned an error for the named specifier: the module failed to load or resolve when the graph was built. Static (import statement) failures abort eszip creation; dynamic imports are tolerated and skipped (the function returns Ok(None)).

Source

Thrown at libs/eszip/v2.rs:1377

      npm_snapshot: &ValidSerializedNpmResolutionSnapshot,
    ) -> Result<
      Option<Box<dyn DoubleEndedIterator<Item = ToVisit<'a>> + 'a>>,
      anyhow::Error,
    > {
      let module = match graph.try_get(visited.specifier()) {
        Ok(Some(module)) => module,
        Ok(None) => {
          return Err(anyhow::anyhow!(
            "module not found {}",
            visited.specifier()
          ));
        }
        Err(err) => {
          if visited.is_dynamic() {
            // dynamic imports are allowed to fail
            return Ok(None);
          }
          return Err(anyhow::anyhow!(
            "failed to load '{}': {}",
            visited.specifier(),
            err
          ));
        }
      };

      let specifier_key =
        resolve_specifier_key(module.specifier(), relative_file_base)?;
      if modules.contains_key(specifier_key.as_ref()) {
        return Ok(None);
      }

      match module {
        deno_graph::Module::Js(module) => {
          let source: Arc<[u8]>;
          let source_map: Arc<[u8]>;
          match module.media_type {

View on GitHub (pinned to 89f33cbef2)

Solutions

Fix the underlying load error for the named specifier (check URL/file availability, run `deno cache --reload`)
If the module is optional, switch to a dynamic `import()` — eszip skips failing dynamic imports
Re-run the build once the dependency is reachable again

Example fix

// before — static import of an occasionally unavailable module
import { x } from "https://example.com/flaky/mod.ts";

// after — dynamic import; eszip tolerates its failure
const { x } = await import("https://example.com/flaky/mod.ts");

Defensive patterns

Strategy: try-catch

Validate before calling

# surface load errors before the eszip step
deno cache --reload entry.ts && deno compile entry.ts

Try / catch

match build_eszip(graph, npm_packages) {
  Err(e) if e.to_string().starts_with("failed to load '") => {
    // extract the failing specifier from the message, report it,
    // or fall back to a previously built artifact
    report_and_fallback(e)
  }
  result => result?,
}

Prevention

Cache and verify remote dependencies (`deno cache --reload`) before compile/bundle steps
Use dynamic import() for optional dependencies — eszip tolerates their failure
Pin remote modules to immutable versioned URLs to avoid 404 drift

When it happens

Trigger: A static import of a module that failed to load — 404 remote URL, unreadable local file, unsupported scheme — while building the eszip/compiled binary.

Common situations: Network failures during `deno compile` of remote dependencies; a file renamed after the graph was cached; importing a URL that now serves an error page.

Related errors

AI-assisted analysis of denoland/deno@89f33cbef2 (2026-08-16). Data as JSON: /api/errors/94d04d2627594491. Report an issue: GitHub.