refactor(lib/withESI): improve types, add safeRequireServer, isClient…

… and isServer functions

lib/src/withESI.tsx

@@ -1,16 +1,18 @@
 import PropTypes from "prop-types";
-import type {
-  ComponentClass,
-  ComponentType,
-  JSX,
-  WeakValidationMap
-} from "react";
-import { Component } from "react";
+import type { WeakValidationMap, ComponentType, ComponentClass } from "react";
+import React from "react";
 
 declare global {
   interface Window {
     __REACT_ESI__: { [s: string]: object };
   }
+
+  // eslint-disable-next-line @typescript-eslint/no-namespace
+  namespace NodeJS {
+    interface Process {
+      browser?: boolean;
+    }
+  }
 }
 
 interface IWithESIProps {
@@ -20,6 +22,31 @@ interface IWithESIProps {
     };
   };
 }
+
+// Prevent bundlers to bundle server.js
+const safeRequireServer = () => {
+  try {
+    // Necessary for NextJS
+    return eval("require('react-esi/lib/server')");
+  } catch (error) {
+    // Necessary for Express and others
+    return eval("require('./server')");
+  }
+};
+
+const isClient = () => {
+  return (
+    (typeof process !== "undefined" && process?.browser) ||
+    typeof window !== "undefined"
+  );
+};
+
+const isServer = () => !isClient();
+
+interface State {
+  childProps: object;
+  initialChildPropsLoaded: boolean;
+}
 /**
  * Higher Order Component generating a <esi:include> tag server-side,
  * and rendering the wrapped component client-side.
@@ -28,19 +55,19 @@ export default function withESI<P>(
   WrappedComponent: ComponentType<P>,
   fragmentID: string
 ): ComponentClass<IWithESIProps & P> {
-  return class WithESI extends Component<P & IWithESIProps> {
+  return class WithESI extends React.Component<P & IWithESIProps, State> {
     public static WrappedComponent = WrappedComponent;
     public static displayName = `WithESI(${
       WrappedComponent.displayName || WrappedComponent.name || "Component"
     })`;
     public static propTypes = {
       esi: PropTypes.shape({
-        attrs: PropTypes.objectOf(PropTypes.string) // extra attributes to add to the <esi:include> tag
-      })
+        attrs: PropTypes.objectOf(PropTypes.string), // extra attributes to add to the <esi:include> tag
+      }),
     } as unknown as WeakValidationMap<IWithESIProps & P>;
-    public state = {
+    public state: State = {
       childProps: {},
-      initialChildPropsLoaded: true
+      initialChildPropsLoaded: true,
     };
     private esi = {};
 
@@ -50,15 +77,15 @@ export default function withESI<P>(
       this.esi = esi || {};
       this.state.childProps = childProps;
 
-      if (typeof window === "undefined") {
+      if (isServer()) {
         return;
       }
 
       if (window.__REACT_ESI__?.[fragmentID]) {
         // Inject server-side computed initial props
         this.state.childProps = {
           ...window.__REACT_ESI__[fragmentID],
-          ...this.state.childProps
+          ...this.state.childProps,
         };
         return;
       }
@@ -81,21 +108,22 @@ export default function withESI<P>(
         .then((initialProps: object) =>
           this.setState({
             childProps: initialProps,
-            initialChildPropsLoaded: true
+            initialChildPropsLoaded: true,
           })
         );
     }
 
     public render() {
-      if (typeof window !== "undefined") {
+      if (isClient()) {
         return (
           <WrappedComponent
             {...(this.state.childProps as JSX.IntrinsicAttributes & P)}
           />
         );
       }
-      // Prevent Webpack and other bundlers to ship server.js
-      const server = eval('require("./server")');
+
+      const server = safeRequireServer();
+
       return server.createIncludeElement(fragmentID, this.props, this.esi);
     }
   };