Add element from one page to different page

Question

How can I create an element with one html/js project but then add it to a completely separate project html document?

Html/js (Project1)
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Create element with Project1.js
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Add element to project2.html with Project1.js
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Html (Project2)

Answer 1

You should take that JavaScript is a client-sided programming language into your mind, when making things such as this.
You could load the script into your site using <script src="file.js"></script> and use some ES6 to export contents of the JS files and make use of it easily.