text: const Event = require('events');
  const ev = new Event();
  
  //订阅
  ev.on('price', (a, b) => {
    console.log(a, b, '涨价了');
  })
  ev.on('price', (a, b) => {
    console.log(a, b, '涨价了');
  })
  
  //发布
  ev.emit('price', '猪肉', '排骨');