重复引用require("babel-polyfill")可能出现的问题

[i5ting]

➜  koa-demo runkoa index.js 
index.js
/Users/sang/workspace/17koa/koa-demo/node_modules/babel-polyfill/lib/index.js:14
  throw new Error("only one instance of babel-polyfill is allowed");
  ^

Error: only one instance of babel-polyfill is allowed
    at Object.<anonymous> (/Users/sang/workspace/17koa/koa-demo/node_modules/babel-polyfill/lib/index.js:14:9)
    at Module._compile (module.js:434:26)
    at Module._extensions..js (module.js:452:10)
    at Object.require.extensions.(anonymous function) [as .js] (/Users/sang/workspace/github/runkoa/node_modules/babel-register/lib/node.js:134:7)
    at Module.load (module.js:355:32)
    at Function.Module._load (module.js:310:12)
    at Module.require (module.js:365:17)
    at require (module.js:384:17)
    at Object.<anonymous> (index.js:3:1)
    at Module._compile (module.js:434:26)
➜  koa-demo cat index.js 
'use strict';

require("babel-polyfill");

// set babel in entry file
require('babel-core/register')({
  presets: ['es2015-node5', 'stage-3']
});

require('./app'); // this is es7 - gets transpiled

[i5ting]

这时正确的操作是

runkoa  app.js