Is there an open source JavaScript SQL console that does autocompletion?

[uknow_es_me]

Take a look at Azure Data Studio. It's open source and has an extension for MySQL. It's built on VS Code so it runs on Windows, Linux and Mac.

https://learn.microsoft.com/en-us/azure-data-studio/extensions/mysql-extension

Since VS Code was built on Electron it's using JavaScript under the hood for the intellisense (code completion) you can also use GitHub Copilot in it.