How do I write ajax paths from passing values to php classes?

How do I write ajax paths from passing values to php classes? A php class, $ tool = new tool ();
Index.html
Use ajax to transmit data to the find method of the php class.
How do I write a path?
Can ajax be used like this?

Reply to discussion (solution)

Transfer your php page wherever it is

Transfer your php page wherever it is

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I need to upload the method to the class. how can I write this path? I certainly know the path of the PHP file, or how can the method in the class accept the data transmitted by ajax?

All requests (including ajax, of course) can only go to the page
The page performs the corresponding action based on the input parameters.

All requests (including ajax, of course) can only go to the page
The page performs the corresponding action based on the input parameters.

So we can only call the method in the initial method and return data.

$ O = new Class;
$ O-> finf ();

That's all right?

Ajax is handled in the same way as link and form submission.