Javascript DOM: Setting custom DOM element properties

Question

Is it ok to set custom properties on DOM elements, and rely on them persisting?

For example, given

 
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Answer 1

This is what the specs say about the internal property accessors:

Host objects may implement these internal methods in any manner unless specified otherwise; for example, one possibility is that [[Get]] and [[Put]] for a particular host object indeed fetch and store property values but [[HasProperty]] always generates false.

and

Host objects may define additional constraints upon [[Put]] operations. If possible, host objects should not allow [[Put]] operations in situations where this definition of [[CanPut]] returns false.

However, I think this is just theoretical, and in reality expandos work as expected.