So the first fact section in this HTML import article states that html imports know better than to request (and execute - if javascript) resources multiple times.
This works within the framework of HTML imports but doesn't work for other type of imports (as in javascript). In this network view of the devtools you can see Polymer.html being loaded first from javascript (d3.js) then again from HTML imports (my-app.html) which I wasn't expecting.
Is there a way to explicitly tell HTML imports that a resource has already been loaded (as in from javascript in this case)?
If I understand this correctly, you are having script file load multiple times because they are called in multiple elements. Please correct me if this is not right.
I do see that the HTML file is what is being parsed twice but the script inside it is actually pulled from cache (on the second reference). If you don't want the HTML file to be parsed again, you'll need to setup caching for the HTML at the server or Service Worker level.
来源：https://stackoverflow.com/questions/28993429/html-import-not-deduping