Questions about how PHP gets the Ajax value.

Questions about how PHP gets the Ajax value ....
Now you have the following questions
1, on the test.php page there is a , test as follows:
10
20
30



Then there is a variable on this page $arr

Now I want to assign the value of option to $arr, and change the value of $arr every time the option is changed.
Then I used Ajax to return the JSON value, each time I changed option, the values were 10,20,30.
My question is how to pass the value of Ajax to $arr.
------Solution--------------------
Ajax to modify a value on the main interface, you can use JS to get rid of the value on the page
Anyway, Ajax is also JS execution, directly in the callback function to add the statement line
Specifically, add a div or span to set an ID, and then write a JS statement
To change the value of a lot of words, simply replace the entire page content.

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