How to link frontend react app to backend?

Question

Yii

How to connect frontend (in React) and backend (in Yii)? The bottom line: there is a frontend that includes a large form with fields: inputs, chboxes, text fields, etc. ... arrays of data for processing in the form are passed to me as a JSON file... no problem with that... problems with validation - it's implemented using Yii but how do I connect it with the react application if I initially render the entire page in 1 tag? Bagkender can't work with inputs because he doesn't see them from the beginning... please explain on your fingers)

Answer 1

make an API.
The frontend should call on the methods that the backend will provide and develop.
It will look like this

//front: 
data = {"id":1,"name":"someName"}; //....
apiUrl = "/users/"+data.id; 
sendAjax(apiUrl, data);
//back: 
UsersController {
   function actionUpdate($id) {
      //load POST  
   }
}

To describe the api, it is recommended to use Swagger