mock.js

  // imagine this is the place where you usually 
	// get the response in the normal application 
	// you need just to pass here result variable
	// it will create a .txt file with the json 
	// and download it. You need just to reuse this
	// mock file later. 
  const element = document.createElement('a');
   
  element.setAttribute('href', 'data:text/plain;charset=utf-8,' + encodeURIComponent(JSON.stringify(results, null, ' ')));
  element.setAttribute('download', 'data.txt');
  element.style.display = 'none';

  document.body.appendChild(element);
  element.click();
  document.body.removeChild(element);