Jonathan Watt pointed out some preferences you can set to ensure that the JavaScript code in your extension is “clean.”
javascript.options.showInConsole set to true causes chrome JavaScript errors to be displayed in the JavaScript console. This preference is essential when you are writing/debugging your extension. If you don’t have it set, your extension will simply not work and you won’t know why.
javascript.options.strict set to true causes JavaScript to parsed in such a way such that you will see errors about bad code on the console. If I had set this preference, I would have found my problem.