Fix error handling

src/pyodide.js

@@ -159,6 +159,7 @@ var languagePluginLoader = new Promise((resolve, reject) => {
             window.pyodide.loadedPackages[package] = toLoad[package];
           }
           delete window.pyodide._module.monitorRunDependencies;
+          window.removeEventListener('error', windowErrorHandler);
           if (!isFirefox) {
             preloadWasm().then(() => {resolve(`Loaded ${packageList}`)});
           } else {
@@ -167,6 +168,17 @@ var languagePluginLoader = new Promise((resolve, reject) => {
         }
       };
 
+      // Add a handler for any exceptions that are thrown in the process of
+      // loading a package
+      var windowErrorHandler = (err) => {
+        delete window.pyodide._module.monitorRunDependencies;
+        window.removeEventListener('error', windowErrorHandler);
+        // Set up a new Promise chain, since this one failed
+        loadPackagePromise = new Promise((resolve) => resolve());
+        reject(err.message);
+      };
+      window.addEventListener('error', windowErrorHandler);
+
       for (let package in toLoad) {
         let script = document.createElement('script');
         let package_uri = toLoad[package];
@@ -280,8 +292,7 @@ var languagePluginLoader = new Promise((resolve, reject) => {
 
   Module.checkABI = function(ABI_number) {
     if (ABI_number !== parseInt('{{ABI}}')) {
-      console.error(`ABI numbers differ. Expected {{ABI}}, got ${ABI_number}`);
+      throw `ABI numbers differ. Expected {{ABI}}, got ${ABI_number}`;
-      return false;
     }
     return true;
   };

test/test_package_loading.py

@@ -132,6 +132,14 @@ def test_different_ABI(selenium_standalone):
     finally:
         (build_dir / 'numpy-broken.js').unlink()
 
+    selenium_standalone.load_package('kiwisolver')
+    selenium_standalone.run('import kiwisolver')
+    assert (
+        selenium_standalone.run('repr(kiwisolver)') ==
+        "<module 'kiwisolver' from "
+        "'/lib/python3.7/site-packages/kiwisolver.so'>"
+    )
+
 
 def test_load_handle_failure(selenium_standalone):
     selenium = selenium_standalone