Merge pull request #3129 from jtpio/tutorial-lab3

Update the custom widget tutorial for JupyterLab 3.0

Author: jtpio

Diff for: docs/source/examples/Widget Custom.ipynb

@@ -53,7 +53,7 @@
     "To create the environment, execute the following command:\n",
     "\n",
     "```bash\n",
-    "conda create -n ipyemail -c conda-forge jupyterlab cookiecutter nodejs python\n",
+    "conda create -n ipyemail -c conda-forge jupyterlab cookiecutter nodejs yarn python\n",
     "```\n",
     "\n",
     "Then activate the environment with:\n",
@@ -120,7 +120,26 @@
     "\n",
     "You also need to enable the widget frontend extension.\n",
     "\n",
-    "If you are using JupyterLab 2.x:\n",
+    "If you are using JupyterLab 3.x:\n",
+    "\n",
+    "\n",
+    "```bash\n",
+    "# link your development version of the extension with JupyterLab\n",
+    "jupyter labextension develop . --overwrite\n",
+    "\n",
+    "# rebuild extension Typescript source after making changes\n",
+    "yarn run build\n",
+    "```\n",
+    "\n",
+    "It is also possible to rebuild the widget automatically when there is a new change, using the `watch` script:\n",
+    "\n",
+    "```bash\n",
+    "# watch the source directory in one terminal, automatically rebuilding when needed\n",
+    "yarn run watch\n",
+    "```\n",
+    "\n",
+    "\n",
+    "If you are using JupyterLab 2.x, you will need to install the `@jupyter-widgets/jupyterlab-manager` extension manually:\n",
     "\n",
     "```bash\n",
     "# install the widget manager to display the widgets in JupyterLab\n",
@@ -802,5 +821,5 @@
   }
  },
  "nbformat": 4,
- "nbformat_minor": 2
+ "nbformat_minor": 4
 }