How to pass a variable (value) from javascript to php?

Question

PHP

Hello I need to pass a variable from app.js file to index.php file and work with variable value already in php code. How to do this without rebooting or as quickly as possible.
Here's the thing for me. I request a qrcode from the user, decrypt and get a set of numbers (This is using JS), after that I send it to PHP. Next, Php makes a request to the database, finds out if this value is there and sends the result of the check back.
The difficulty is that I do not understand how to pass a variable without clicking on the button. Tell me please!

Answer 1

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How to pass variable value from js to php?
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