how to enable the JavaScript for Favorites list page

Summary:

We want to enable/disable the "Next/Create Quote" button on the favorites page based on the number of favorites selected by user.

We had written the java script code and it is working in console but when we keep the same code in footer html it is not working as script is not able to find the button id

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Version (include the version you are using, if applicable):

24A

Code Snippet (add any code snippets that support your topic, if applicable):

Below code is working in console. We are getting null when we keep the same in footer html