Use object keys to prevent accidental iteration over prototype properties

Author: ValentaTomas

js/src/code-interpreter.ts

@@ -231,8 +231,7 @@ export class JupyterExtension {
    * Close all the websocket connections to the kernels. It doesn't shutdown the kernels.
    */
   async close() {
-    // TODO: For in check
-    for (const kernelID in this.connectedKernels) {
+    for (const kernelID of Object.keys(this.connectedKernels)) {
       this.connectedKernels[kernelID].close()
     }
   }

js/src/messaging.ts

@@ -113,8 +113,7 @@ export class Data {
     this.raw = data
 
     this.extra = {}
-    // TODO: For in check
-    for (const key in data) {
+    for (const key of Object.keys(data)) {
       if (![
         'text/plain',
         'text/html',