Disable the submit button once clicked

[masakudamatsu]

To feedback the user about something going on as a response to the user's click action.

"Say a button does something pretty darn important, like submitting a payment. It would be pretty scary if it was programmed such that clicking the button multiple times submitted multiple payment requests. It is situations like this where you would attach a click handler to a button that only runs once. To make that clear to the user, we'll disable the button on click as well." -- CSS Tricks

For how to test-drive this, see https://www.evernote.com/l/AFN4F0X9fYxDL5-dE_qMzzMbC5EOYbTQ01U