TypeError: compiler.plugin is not a function

const path = require('path');
const MyWebpackPlugin = require("./my-webpack-plugin");

module.exports = {
   mode : 'development',
   entry: {
       main: './src/app.js'
   },
   output: {
       path: path.resolve('./dist'),
       filename: '[name].js'
   },
   module : {
       rules : [
           {
               test: /\.css$/,
               use: [
                   'style-loader',
                   'css-loader'
               ]
           },
           {
               test: /\.(png|jpg|gif|svg)$/,
               loader: 'url-loader',
               options: {
                   publicPath: './dist/',
                   name: '[name].[ext]?[hash]',
                   limit: 20000,
               }
           }
       ]
   },
   plugins: [
       new MyWebpackPlugin()
   ]
}

class MyWebpackPlugin {
    apply(compiler) {
        /*compiler.hooks.done.tap("My Plugin", stats => {
            console.log("MyPlugin: done")
        })*/

        compiler.plugin('emit', (compilation, callback) => { 
            const source = compilation.assets['main.js'].source();

            compilation.assets['main.js'].source = () => {
                const banner = [
                    '/**',
                    ' * 이것은 BannerPlugin이 처리한 결과입니다.',
                    ' * Build Date: 2019-10-10',
                    ' */'
                ].join('\n');
                return banner + '\n' + source;
            }

            callback();
        })
    }
}

module.exports = MyWebpackPlugin;

플러그인 부분 따라서 공부하던 중 class myWebpackPlugin을 블로그 소스로 가져온 뒤에 npm run build를 돌렸는데여,

[webpack-cli] TypeError: compiler.plugin is not a function

이런 에러가 발생했어여ㅠ_____ㅠ 왜 그러는걸까여?