Merge pull request #3590 from blink1073/fix-dev-mode-stripe

Fix handling of dev mode

CONTRIBUTING.md

@@ -114,8 +114,9 @@ jupyter lab --dev-mode
 ```
 
 Development mode ensures that you are running the JavaScript assets that are
-built in the dev-installed Python package.  When running from source in development
-mode, the page will have a red stripe at the top to indicate it is an unreleased version.
+built in the dev-installed Python package.  When running in dev mode, a red
+stripe will appear at the top of the page; this is to indicate running
+an unreleased version.
 
 ### Build and run the tests
 

packages/application/src/index.ts

@@ -63,7 +63,7 @@ class JupyterLab extends Application<ApplicationShell> {
   constructor(options: JupyterLab.IOptions = {}) {
     super({ shell: new ApplicationShell() });
     this._info = { ...JupyterLab.defaultInfo, ...options };
-    if (options.devMode) {
+    if (this._info.devMode) {
       this.shell.addClass('jp-mod-devMode');
     }