Using javascript to populate a list column on newform.aspx

I have a custom newform.aspx sharepoint list where I want to populate a certain column based on what URL the user came from.

Is javascript the best way to do this?

So the logic goes,

If incoming link = "social.msn.com" then set Issue Category field = "essbase"

 else end if.

Thanks.

I would like to format this logic into java.