Fix #1493: Don't crash when the reps error out (#1513)

* Fix #1493: Don't crash when the reps error out

* Put handler in ValueRenderer.  Provide information about error.

* Also display `toString`

src/components/reps/value-renderer.jsx

@@ -11,8 +11,35 @@ export default class ValueRenderer extends React.Component {
     valueToRender: PropTypes.any
   };
 
+  constructor(props) {
+    super(props);
+    this.state = {};
+  }
+
+  componentDidCatch(error, errorInfo) {
+    this.setState({ error, errorInfo });
+  }
+
   render() {
     const value = this.props.valueToRender;
+
+    if (this.state.errorInfo) {
+      return (
+        <div>
+          <pre>{value.toString()}</pre>
+          <h2>A value renderer encountered an error.</h2>
+          <pre>
+            {this.state.error && this.state.error.toString()}
+            <br />
+            {this.state.errorInfo.componentStack}
+          </pre>
+          <a href="https://github.com/iodide-project/iodide/issues/new">
+            Please file a bug report.
+          </a>
+        </div>
+      );
+    }
+
     const htmlString = UserReps.getUserRepIfAvailable(value);
     if (htmlString) {
       return <HTMLHandler htmlString={htmlString} />;