fix: Add some code splitting for PWA build (#937)

* fix: Add some code splitting for PWA build

* Fix missing files

extensions/dicom-microscopy/src/DicomMicroscopyViewport.js

@@ -1,10 +1,7 @@
 import React, { Component } from 'react';
 import ReactResizeDetector from 'react-resize-detector';
-import { api } from 'dicom-microscopy-viewer';
 import debounce from 'lodash.debounce';
 
-const microscopyViewer = api.VLWholeSlideMicroscopyImageViewer;
-
 class DicomMicroscopyViewport extends Component {
   state = {
     error: null,
@@ -56,9 +53,12 @@ class DicomMicroscopyViewport extends Component {
         }
         return Promise.all(promises);
       })
-      .then(metadata => {
+      .then(async metadata => {
         metadata = metadata.filter(m => m);
 
+        const { api } = await import(/* webpackChunkName: "dicom-microscopy-viewer" */ 'dicom-microscopy-viewer');
+        const microscopyViewer = api.VLWholeSlideMicroscopyImageViewer;
+
         this.viewer = new microscopyViewer({
           client: dicomWebClient,
           metadata,

extensions/dicom-microscopy/src/asyncComponent.js

@@ -0,0 +1,37 @@
+/**
+ * We use this component to leverage "Code Splitting"
+ *
+ * Link: https://serverless-stack.com/chapters/code-splitting-in-create-react-app.html
+ */
+
+import React, { Component } from 'react';
+
+export default function asyncComponent(importComponent) {
+  class AsyncComponent extends Component {
+    constructor(props) {
+      super(props);
+
+      this.state = {
+        component: null,
+      };
+    }
+
+    async componentDidMount() {
+      // Add dynamically loaded component to state
+      const { default: component } = await importComponent();
+
+      this.setState({
+        component: component,
+      });
+    }
+
+    render() {
+      const C = this.state.component;
+
+      // Render the loaded component, or null
+      return C ? <C {...this.props} /> : null;
+    }
+  }
+
+  return AsyncComponent;
+}

extensions/dicom-microscopy/src/index.js

@@ -1,5 +1,11 @@
+import asyncComponent from './asyncComponent.js';
 import DicomMicroscopySopClassHandler from './DicomMicroscopySopClassHandler.js';
-import DicomMicroscopyViewport from './DicomMicroscopyViewport.js';
+
+const DicomMicroscopyViewport = asyncComponent(() =>
+  import(
+    /* webpackChunkName: "DicomMicroscopyViewport" */ './DicomMicroscopyViewport.js'
+  )
+);
 
 export default {
   /**