feat: support webpack 4

Author: yibn2008

lib/index.js

@@ -195,21 +195,44 @@ class FastCSSSplitWebpackPlugin {
    * @returns {void}
    */
   apply (compiler) {
-    if (this.options.defer) {
-      // Run on `emit` when user specifies the compiler phase
-      // Due to the incorrect css split + optimization behavior
-      // Expected: css split should happen after optimization
-      compiler.plugin('emit', (compilation, done) => {
-        return this.chunksMapping(compilation, compilation.chunks, done)
-      })
+    // for webpack 4
+    if (compiler.hooks) {
+      const plugin = {
+        name: 'FastCssSplitPlugin'
+      }
+
+      if (this.options.defer) {
+        // Run on `emit` when user specifies the compiler phase
+        // Due to the incorrect css split + optimization behavior
+        // Expected: css split should happen after optimization
+        compiler.hooks.emit.tapAsync(plugin, (compilation, done) => {
+          this.chunksMapping(compilation, compilation.chunks, done)
+        })
+      } else {
+        // use compilation instead of this-compilation, just like other plugins do
+        compiler.hooks.compilation.tap(plugin, compilation => {
+          compilation.hooks.optimizeChunkAssets.tapAsync(plugin, (chunks, done) => {
+            console.log('----- fast-css-split-plugin')
+            this.chunksMapping(compilation, chunks, done)
+          })
+        })
+      }
     } else {
-      // Only run on `this-compilation` to avoid injecting the plugin into
-      // sub-compilers as happens when using the `extract-text-webpack-plugin`.
-      compiler.plugin('this-compilation', (compilation) => {
-        compilation.plugin('optimize-chunk-assets', (chunks, done) => {
-          return this.chunksMapping(compilation, chunks, done)
+      if (this.options.defer) {
+        // Run on `emit` when user specifies the compiler phase
+        // Due to the incorrect css split + optimization behavior
+        // Expected: css split should happen after optimization
+        compiler.plugin('emit', (compilation, done) => {
+          return this.chunksMapping(compilation, compilation.chunks, done)
         })
-      })
+      } else {
+        // use compilation instead of this-compilation, just like other plugins do
+        compiler.plugin('compilation', (compilation) => {
+          compilation.plugin('optimize-chunk-assets', (chunks, done) => {
+            return this.chunksMapping(compilation, chunks, done)
+          })
+        })
+      }
     }
   }
 }