exportAsJSON.js

function exportAsJSON(fileName, myJsonObject){
  var data = "text/json;charset=utf-8," + encodeURIComponent(JSON.stringify(myJsonObject));
  var a = document.createElement('a');
  a.href = "data: "+data;
  a.download = fileName+".json";
  a.click();
}

var someData = {
  name: "John",
  age: 23
}

exportAsJSON("john", someData);