Why should people use multiple versions of jQuery on the same page?

Question

I noticed that sometimes people have to use multiple versions of jQuery on the same page (see question 1 and question 2 ). I assume that people should migrate older versions of jQuery because some parts of their code are based on an older version of jQuery. Obviously, this approach leads to inefficiencies. The ideal solution is to reorganize the old code to use the new jQuery API. I wonder if there are tools that automate the process of updating a piece of code to use the newer version of jQuery. I have never written programs in Javascript or jQuery. Therefore, I would like to hear from programmers with experience in this language my opinion on this issue. In particular, I would like to know the following.

• How difficult is it to download multiple versions of jQuery?
• Have you ever downloaded multiple versions of any other library on one page?
• Do you know any refactoring tool that helps you port your code to use the updated API?
• Do you think such a refactoring tool is useful? Do you want to use it?

Please do not consider this question closed. The current answers have already given me a good idea of ​​the process and tools available for updating jQuery code. But please feel free to add your own experience when updating jQuery code.

Answer 1

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Answer 2

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Answer 3

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