[throwanem]

The FileReader web API enables you to make local files available to content running in the browser. This entails a file picker and, depending on the verbiage in your browser UI, that may talk about "upload." That doesn't mean anything is being sent anywhere. See MDN: https://developer.mozilla.org/en-US/docs/Web/API/FileReader

(Or that nothing is; I have not audited this code. But I vouched the parent comment to point out that browsers do offer this capability, and there's nothing facially suspicious in claiming to use it.)

[wainguo]

Great explanation!

Maybe I should not use the text ’upload’ to avoid the confusion

[throwanem]

Oh, I see it there in your copy. Yes, I would use a different verb there, such as "pick" or "choose" or "select."

[brightbeige]

“open”