[next] Include most basic error plugin (#1677)

pyscript.core/src/plugins/error.js

@@ -0,0 +1,40 @@
+// PyScript Error Plugin
+import { hooks } from "../core.js";
+
+hooks.onBeforeRun.add(function override(pyScript) {
+    // be sure this override happens only once
+    hooks.onBeforeRun.delete(override);
+
+    // trap generic `stderr` to propagate to it regardless
+    const { stderr } = pyScript.io;
+
+    // override it with our own logic
+    pyScript.io.stderr = (...args) => {
+        // grab the message of the first argument (Error)
+        const [{ message }] = args;
+        // show it
+        notify(message);
+        // still let other plugins or PyScript itself do the rest
+        return stderr(...args);
+    };
+});
+
+// Error hook utilities
+
+// Custom function to show notifications
+function notify(message) {
+    const div = document.createElement("div");
+    div.className = "py-error";
+    div.textContent = message;
+    div.style.cssText = `
+    border: 1px solid red;
+    background: #ffdddd;
+    color: black;
+    font-family: courier, monospace;
+    white-space: pre;
+    overflow-x: auto;
+    padding: 8px;
+    margin-top: 8px;
+  `;
+    document.body.append(div);
+}