A "supported" way to manipulate main views with Javascript

Here I will describe a "supported" way to manipulate main views with Javascript in Microsoft Dynamics CRM. That is, how to get my own Javascript into a main view.
When searching the web and asking some people it seemed not possible to do this without either editing the aspx pages or use advanced technologies like implementing a http handler, which is all definitely unsupported. But, late at night, when I couldn't sleep (don't worry, it was not because of this subject), I thought of a solution which is not unsupported (at least, not that unsupported)...

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