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Boostnote is an Electron app so it's based on Chromium; developers can use Developer Tools just like Google Chrome.
You can toggle the Developer Tools like this:
The Developer Tools will look like this:
When errors occur, the error messages are displayed at the console.
For example, you can use the debugger to set a breakpoint in the code like this:
This is just an illustrative example, you should find a way to debug which fits your style.