通过实例学习是最快的，让我们看一个最简单的例子，webpack-clear-console，这个插件是去除输出里的 console 调用，里面插件的写法是 webpack4 之前的写法，不过基本上是一致的，通过源码可以看到插件在 emit 这个钩子上（生成资源到output目录之前）触发，通过 compilation 对象的 assets 对象的 source 方法获取文件内容，然后进行正则匹配。 最后需要将 source 和 size 的变动归回原来的 compilation 对象中，否则这些变动是不会生效的
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    1. var WebpackClearConsole = function () {
    2. };
    4. WebpackClearConsole.prototype.apply = function (compiler) {
    5.     var self = this;
    7.     compiler.plugin("emit", function (compilation, callback) {
    8.         compilation.chunks.forEach(function (chunk) {
    10.             // Explore each asset filename generated by the chunk and replace the console.* methods:
    11.             chunk.files.forEach(function (filename) {
    13.                 // Get the asset source for each file generated by the chunk:
    14.                 var source = compilation.assets[filename].source();
    16.                 var consoleName=["console","window.console"];
    17.                 var consoleType= ["log", "info", "warn", "error" ,"assert" ,"count" ,"clear", "group" ,
    18.                     "groupEnd", "groupCollapsed" ,"trace" ,"debug", "dir" ,"dirxml", "profile", "profileEnd" ,
    19.                     "time" ,"timeEnd" ,"timeStamp" ,"table","exception"];
    21.                 //Console.log|debug|info|warn|error regexp
    22.                 rConsole = new RegExp("(" + consoleName.join("|") + ")" + ".(?:" + consoleType.join("|") + ")\\s{0,}\\([^;]*\\)(?!\\s*[;,]?\\s*\\/\\*\\s*NotClearConsole\\s*\\*\\/)\\s{0,};?", "gi");
    24.                 //Regexp replace null
    25.                 source = source.replace(rConsole, function() {
    26.                     return source.replaceWith || "";
    27.                 });
    29.                 compilation.assets[filename] = {
    30.                     source: function () {
    31.                             return source;
    32.                         },
    33.                     size: function () {
    34.                             return source.length;
    35.                         }
    36.                 }
    37.             });
    38.         });
    39.         callback();
    40.     });
    41. };
    43. module.exports = WebpackClearConsole;