vue-hello/node_modules/@vue/babel-helper-vue-transform-on/index.js

const transformOn = (obj) => {
  const result = {};
  Object.keys(obj).forEach((evt) => {
    result[`on${evt[0].toUpperCase()}${evt.substr(1)}`] = obj[evt];
  });
  return result;
};

module.exports = transformOn;