simple regex validation, readme 💄

Author: jrieken

Diff for: README.md

@@ -1,10 +1,20 @@
-Sample notebook for VS Code that renders regular expressions using https://regexper.com.
+Native notebook for VS Code that renders regular expressions using https://regexper.com.
 
 
-![Sample showing rendered regular expression](img.png)
+![Sample showing rendered regular expression](https://github.com/jrieken/vscode-regex-notebook/raw/master/img.png)
+
+This samples makes use of the following APIs/concepts
+
+* `NotebookSerializer` to load and save notebook documents from disk
+* `NotebookController` to execute regular expressions cells
+* `NotebookRenderer` to present regular expressions in a nice way
 
 ### Running out of source
 
 * run `npm install` in the terminal
 * also run `npm run compile`
 * select `F5` to debug
+
+### Thanks
+
+The rendering uses the https://regexper.com source code which works like a charme 👏 

Diff for: src/extension/extension.ts

@@ -60,6 +60,25 @@ export function activate(context: vscode.ExtensionContext) {
 			const execution = controller.createNotebookCellExecution(cell);
 			execution.start();
 			const cellContent = execution.cell.document.getText();
+
+			try {
+				// "validation" by parsing
+				const match = /\/(.*)\/(.*)/.exec(cellContent);
+				if (match) {
+					new RegExp(match[1], match[2]);
+				} else {
+					new RegExp(cellContent);
+				}
+			} catch (err) {
+				// show validation error and continue with next cell
+				const errorItem = vscode.NotebookCellOutputItem.error(err as Error);
+				const regexOutput = new vscode.NotebookCellOutput([errorItem]);
+				execution.replaceOutput(regexOutput);
+				execution.end(false);
+
+				continue;
+			}
+
 			const regexItem = vscode.NotebookCellOutputItem.text(cellContent, 'application/x.regexp');
 			const regexOutput = new vscode.NotebookCellOutput([regexItem]);
 			execution.replaceOutput(regexOutput);