Question how to use javascript variable for php.

That code stored on the server is interpreted/executed by the server's PHP program. From PHP's point of view <?Except for the ones in php?>, it's just a String. I don't interpret it and just pass by as if it's commented.So the order, it makes sense to use the PHP variable in the Javascript code, but it doesn't make sense to use the Javascript variable in the PHP code.

I don't know specifically, but I think you're trying to use var price in other invisible JS codes below, but if the flow is like that, set the price to 0, and use asynchronous communication like jQuery.get() or jQuery.post() below, 0 or 1 as the key value of $optionPrice (var some value = 14).After you send...) you can get the value you want, and if you have, you can assign a new value from the server to the price variable that you set to 0.

in a nutshell

JS Code Execution -> PHP Code Execution -> To run JS Code, I think my level of answer is to use asynchronous communication such as,,,jQuery.get(), or jQuery.post(). I hope it was helpful!