How to package the koa2 framework app through webpack? What should I do?

This article introduces to you the steps and final deployment of using webpack to package the koa2 framework. It is very practical. Friends in need can refer to it.

In the past, when I used koa to write servers, publishing was simply It's a nightmare. All files in src need to be overwritten, and the config configuration file must also be overwritten. If you are not careful, various problems will be reported online, and then you have to roll back and adjust them locally before publishing. I accidentally saw an article about how to use webpack to package koa app. I was shocked. It turns out that webpack can also package the backend. I had never thought of this before.

Key issues

1: All modules in node_modules are not packaged

The core function of webpack is to reference Each module is typed into a file, and various standardized modules are unified and modularized (webpack specification).

However, node contains a large number of fs and path operations. These fs and path operations will have no operation objects after the packaging is completed, and many various errors will be reported.

So the core of using webpack for packaging is to refuse to package all modules in node_modules, and only package the files referenced by relative paths into one file. It happened that we found that webapck provides the externals attribute to exclude modules that do not need to be packaged.

If we dig deeper, we can find that modules like webpack, nodemon, and babel-preset-env are packages that the app development environment depends on, and our program will not require these modules at all.

In summary, we can find that: we only need to exclude all required packages. This module corresponds to the module under dependencies in package.json. It is important to understand the difference between dependencies and devDependencies.

So we can use the externals-dependencies plug-in with the externals attribute to exclude dependencies.

Code:

const webpack = require('webpack');
const _externals = require('externals-dependencies')
module.exports = {
  ...
  externals: _externals(),
  ...
}

Two: target points to node

Official documentation: Compiled into a Node.js-like environment available (use Node.js require to load chunk)

Code:

target: 'node',

Three: Add node configuration

Official documentation: These options can configure whether to polyfill or mock certain Node.js Global variables and modules. This allows code originally written for the Node.js environment to run in other environments such as browsers.

Code:

node: {
    console: true,
    global: true,
    process: true,
    Buffer: true,
    __filename: true,
    __dirname: true,
    setImmediate: true,
    path: true
},

Four: babel configuration

In order to be compatible with the problem that lower versions of node do not natively support async/await. Here I use babel-preset-env{"modules": false} configuration for babel. This configuration will convert es6 syntax to es5 syntax, such as let and const to var.

At the same time, all async/await functions are also converted into the _asyncToGenerator function defined in the polyfill.

In fact, promises are used to implement the functions of async functions.

Of course this function also requires the regeneratorRuntime function when running. So I introduced babel-polyfill globally to provide the regeneratorRuntime function.

Note: If your node version is very high and supports async/await natively, you can omit babel-preset-env and babel-polyfill

Code:

const path = require('path');
const webpack = require('webpack');
const _externals = require('externals-dependencies')

module.exports = {
  entry: {
    app: [
      // 如果polyfill放在这里，打包的时候将不会被external,必须在js里require才能有效external
      // 'babel-polyfill',
      './src/index.js'
    ]
  },
  output: {
    path: path.resolve(__dirname),
    filename: '[name].js'
  },
  resolve: {
    extensions: [".js"]
  },
  target: 'node',
  externals: _externals(),
  context: __dirname,
  node: {
    console: true,
    global: true,
    process: true,
    Buffer: true,
    __filename: true,
    __dirname: true,
    setImmediate: true,
    path: true
  },
  module: {
    rules: [
      {
        test: /\.js/,
        use: ['babel-loader']
      }
    ]
  },
  plugins: [
    new webpack.DefinePlugin({
      'process.env': {
        NODE_ENV: '"development"'
      }
    }),
  ]
}

Deployment

After packaging, deployment is much more convenient. You only need to deploy package.json, app.js, and the html in the view online. Then execute

1. npm install
2. npm run for

on the server and then the server will run in the background. If you need to update and publish, you only need to re-package npm run dev or npm run build locally and drag it to the server to overwrite app.js.

The above is what I compiled for everyone. I hope it will be helpful to everyone in the future.

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