Upgrading to a New Edition of a Kindle Book

I bought the 2nd edition of JavaScript & jQuery Missing Manual as a Kindle book in May. Then in October, it came out with a new edition. 1) What are the differences between the 2nd and 3rd edition? Are they large enough that I should upgrade? 2) Do I need to pay full price again? It seems like a waste to have only had the previous edition for a few months before a new one was released.
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