@all
感谢 @Geek_144c1d 同学指出了一个 webpack.config.js 配置的错误，正确的写法应该是：
const merge = require('webpack-merge')
const baseConfig = require('./webpack.base.config')
const devConfig = require('./webpack.dev.config')
const proConfig = require('./webpack.pro.config')

module.exports = (env, argv) => {
    let config = argv.mode === 'development' ? devConfig : proConfig;
    return merge(baseConfig, config);
};

npm run build 报错，是webpack现版本不允许这样配置了吗
Invalid configuration object. Webpack has been initialised using a configuration object that does not match the API schema.
 - configuration has an unknown property 'plugin'. These properties are valid:
   object { amd?, bail?, cache?, context?, dependencies?, devServer?, devtool?, entry?, externals?, infrastructureLogging?, loader?, mode?, module?, name?, node?, optimization?, output?, parallelism?, performance?, plugins?, profile?, recordsInputPath?, recordsOutputPath?, recordsPath?, resolve?, resolveLoader?, serve?, stats?, target?, watch?, watchOptions? }
   For typos: please correct them.
   For loader options: webpack >= v2.0.0 no longer allows custom properties in configuration.
     Loaders should be updated to allow passing options via loader options in module.rules.
     Until loaders are updated one can use the LoaderOptionsPlugin to pass these options to the loader:
     plugins: [
       new webpack.LoaderOptionsPlugin({
         // test: /\.xxx$/, // may apply this only for some modules
         options: {
           plugin: …
         }
       })
     ]

老师，npm start 之后报这个错误，编译失败
ERROR in (webpack)-dev-server/client?http://localhost:8081
Module not found: Error: Can't resolve './overlay' in '/Users/helinpeng/Documents/ts_in_action/node_modules/webpack-dev-server/client'
 @ (webpack)-dev-server/client?http://localhost:8081 10:14-34
 @ multi (webpack)-dev-server/client?http://localhost:8081 ./src/index.js

dev环境运行报如下错误，主要是webpack.dev.config.js写法问题。
Invalid configuration object. Webpack has been initialised using a configuration object that does not match the API schema.
 - configuration has an unknown property 'devtools'. These properties are valid:
   object { amd?, bail?, cache?, context?, dependencies?, devServer?, devtool?,entry?, externals?, infrastructureLogging?, loader?, mode?, module?, name?, node?, optimization?, output?, parallelism?, performance?, plugins?, profile?, recordsInputPath?, recordsOutputPath?, recordsPath?, resolve?, resolveLoader?, serve?, stats?, target?, watch?, watchOptions? }
   For typos: please correct them.
   For loader options: webpack >= v2.0.0 no longer allows custom properties in configuration.
     Loaders should be updated to allow passing options via loader options in module.rules.
     Until loaders are updated one can use the LoaderOptionsPlugin to pass these options to the loader:
     plugins: [
       new webpack.LoaderOptionsPlugin({
         // test: /\.xxx$/, // may apply this only for some modules
         options: {
           devtools: …
         }
       })
     ]
将
module.exports = {
    devtools: 'cheap-module-eval-source-map'
}
更改为
const webpack = require('webpack');
module.exports = {
    plugins: [
        new webpack.LoaderOptionsPlugin({
            options: {
                devtools: 'cheap-module-eval-source-map'
            }
        })
    ]
}
dev就可以正常运行了，不知道是不是webpack版本更新的原因。

let hello : string = "Hello word typescript"
document.querySelectorAll('.app')[0].innerHTML = hello;
document.querySelector('.app').innerHTML = hello;
console.log("document.querySelectorAll('.app')[0]:",document.querySelectorAll('.app')[0])
console.log("document.querySelector('.app'):",document.querySelector('.app'))，为啥，我用querySelector选择器不能点出方法？？