初學webpack，用babel將es6轉化為es5時報錯：ERROR in ./entry.jsModule build failed: Error: Cannot find module 'core-js/library/fn/get-iterator'重裝babel-core也不管用webpack配置為：module.exports = {    entry: './entry.js',    output: {        filename: 'bundle.js'    },    //devtool: 'source-map',    module: {        loaders: [{            test: /\.css$/,            loader: 'style-loader!css-loader'        },{            test: /\.js$/,            exclude: /node_modules/,            loader: 'babel-loader'        }]    }}.babelrc內容為：{"presets": ["es2015"]}entry.js為：var a = require('./a.js');require('./index.css');let app = document.getElementById('app');app.innerHTML = '<p>hello webpack!</p>' + a.a;