JQuery code in another file

befo开发者_如何学JAVAre this I wrote all jquery-code into main fail. Now I want to move it into another js-file. The problem is that it doesn't want work correctly. Here is an error by FireBug:

$ is not defined

$(document).ready(\n

So, as I understand, I have to initialize $-var... But how?

Thanks.

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Include jQuery before the file that uses it.