window fetch overload

fetch_overload.js

 
const {fetch: origFetch} = window;
window.fetch = async (...args) => {
  console.log("fetch called with args:", args);
  const response = await origFetch(...args);
  
  /* work with the cloned response in a separate promise
     chain -- could use the same chain with `await`. */
  response
    .clone()
    .json()
    .then(body => console.log("intercepted response:", body))
    .catch(err => console.error(err))
  ;
    
  /* the original response can be resolved unmodified: */
  //return response;
  
  /* or mock the response: */
  return {
    ok: true,
    status: 200,
    json: async () => ({
      userId: 1,
      id: 1,
      title: "Mocked!!",
      completed: false
    })
  };
};

// test it out with a typical fetch call
fetch("https://jsonplaceholder.typicode.com/todos/1")
  .then(response => response.json())
  .then(json => console.log("original caller received:", json))
  .catch(err => console.error(err))
;