Diagnosing ClojureScript Runtime Issues: Compilation vs. Environment Mismatch

ClojureScript Errors: Is it a Code Bug or a Target Environment Mismatch?

When your ClojureScript code fails in the browser but compiles cleanly, the problem is rarely in the Clojure logic itself; it's usually how the compiled JavaScript interacts with the specific browser or execution environment. The immediate takeaway is to verify the generated JavaScript output against the expected runtime capabilities.

Diagnostic Checklist for Execution Failures

Before debugging application logic, isolate the failure point using this guide:

Ordered Verification Steps

1. Inspect Compilation Output: Run your build tool (e.g., Leiningen or using `deps.edn`) and examine the resulting JavaScript bundle. Confirm that complex Clojure constructs (like data definitions) have been correctly translated into standard JavaScript idioms.
2. Test in Isolation: Load *only* the generated JavaScript file directly in a standard browser console (e.g., Chrome DevTools). Do not run it through the application wrapper yet.
3. Verify Interoperability: If you use JavaScript APIs, ensure the mechanism for calling them (e.g., `js/...` syntax) matches the target environment's availability.

Fixes Based on Findings

If the compilation is sound but execution fails:

• Interop Fix: If a JS function is unavailable, ensure the required library is loaded *before* the ClojureScript code attempts to call it in the HTML entry point.
• Target Fix: If the error relates to missing runtime features, adjust your build configuration to explicitly target the required environment (e.g., ensuring browser polyfills are included if targeting older browsers).

Concrete Example: If your ClojureScript attempts to access `window.localStorage` but fails, check the generated JS. If the call is present but throws, the issue is likely that the browser context hasn't fully loaded the DOM/window object when the script executes, not that ClojureScript failed to compile the call.

Escalation Criteria

Escalate to compiler-specific documentation if:

• The generated JavaScript is syntactically invalid JS.
• Macro expansion results in code that doesn't match expected Clojure semantics, even after verification.

Practical Check: After running the build, open the generated `.js` file and search for a complex Clojure feature you used (e.g., a specific `defmacro`). Confirm its translation into recognizable, valid JavaScript code.