Windows Based Emulator Will Not Launch

[David_Vona]

Is there something wrong with the service that supports the Windows Based Emulator? I was using it yesterday with no issues. Now, I can’t get it started, no matter what I try. I currently have a class full of students and none of them can test their code. They can’t use their personal devices, because of state level phone restrictions. Getting any new sort of emulator software installed will not be a quick process. I’m kind of in a tough spot right now.

[ABG]

FAQ Section: Companion and Emulator

Introductory Your First App Testing - MIT AIStarter for 64 bit Windows - MIT Sample Connect -> Companion sequence - @ABG Breaking News: 3/26/2026 Current Version, from the AI2 Help->Companion Info link: 2.78a Downloadable 2.78u link: https://ai2.appinventor.mit.edu/companions/MITAI2Companion.apk http://ai2.appinventor.mit.edu/companions/MITAI2Companion.apk Prior versions Usage Techniques Check the MIT Rendezvous server status - JIS MIT AIStarter (Connect->Emulator) Companion Update…

[ABG]

In light of yesterday's version update, you probably need to install or upgrade the Companions on your emulators.

Here's an old video showing how to do that.

How to Update the Companion on the MIT AIStarter (Connect->Emulator) emulator

I did some experimenting with AIStarter, and made a couple of videos on how to replace the Companion on the MIT emulator with the current version. To check the Companion version on the MIT emulator: [AIStarter Companion Version Check] To get the latest Companion onto your hard drive: [Get the Companion apk] I like to keep them by version: [Download the Companion to your Downloads folder] This assumes you have already downloaded the latest MITAI2Companion.apk to your hard drive's Downloa…

[hcf2000]

I have the same problem today. When I click "Connect -> Emulator", nothing happens. The aiStarter console does not show any incoming connection attempts.

I have done some extensive troubleshooting and narrowed down the issue to the web frontend. Here is the detailed breakdown:

My Environment:

• OS: Windows 10/11

• Browser: Chrome (v146.0.7680.80) and Firefox

• App Inventor Tools: v3.0.0 / v2.3 (Clean install)

• Antivirus: None (Windows default settings, no third-party web shields blocking localhost)

Troubleshooting Steps Taken:

1. If I manually type http://127.0.0.1:8004/start/ in the browser, the emulator launches perfectly. This confirms that aiStarter, adb.exe, and the emulator image are working correctly.

2. I tested this on the main server, ai2-test, and the code server. The issue is identical across all of them.

3. The issue persists even in Incognito/Private browsing mode.

The Error Log: When I open the Chrome Developer Tools (F12) and click the "Emulator" button, the request never leaves the browser. Instead, the Console is flooded with the following JavaScript crash:

Uncaught TypeError: Cannot read properties of undefined (reading 'XmlHttp') at O (aiblockly-4334f11839034257aba5b6bdd4c0e9e5fc18bb9b474b02760f65aac9eab4e453.cache.js:2051:123)

It appears that the frontend JavaScript is failing to instantiate the XMLHttpRequest object to communicate with localhost, causing the script to crash before sending the command to aiStarter.

Is there a known workaround for this specific JavaScript error, or is this a bug in the current Blockly web deployment? Any guidance would be greatly appreciated!

Thank you.

[David_Vona]

I can confirm I’m getting the same console error.

[hcf2000]

It worked perfectly. Thanks a lot for your help!

[ewpatton]

This bug should be fixed with the nb204a release.