How does php respond to the onclick event of the button?

Php responds to the button onclick event. I use the codeigniter framework in php to reference the smart template. how does the button event controller on the page respond to this issue? thank you. It is best to give an example.

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Asynchronous PHP request using JS

Can you give an example?

Baidu ajax Synchronous Asynchronous interaction technology

W3school, search for the jquery ajax example above.

Index.html button and js execution event

   
   Button click test