Add exports to package.json

Fixes apollographql#11569 apollographql#9925

.changeset/green-roses-flow.md

@@ -0,0 +1,5 @@
+---
+"@apollo/client": patch
+---
+
+Added `exports` field to `package.json` for better ESM interop

config/entryPoints.js

@@ -51,6 +51,10 @@ exports.map = function map(callback, context) {
   return entryPoints.map(callback, context);
 };
 
+exports.reduce = function (callback, context) {
+  return entryPoints.reduce(callback, context);
+};
+
 const path = require("path").posix;
 
 exports.check = function (id, parentId) {

config/prepareDist.js

@@ -38,6 +38,27 @@ delete packageJson.scripts;
 delete packageJson.bundlesize;
 delete packageJson.engines;
 
+packageJson.exports = {
+  ".": {
+    types: packageJson.types,
+    import: packageJson.module,
+    require: packageJson.main,
+  },
+  "./package.json": {
+    default: "./package.json",
+  },
+  ...entryPoints.reduce((acc, { dirs, bundleName = dirs[dirs.length - 1] }) => {
+    if (!dirs.length) return acc;
+    let path = `./${dirs.join("/")}`;
+    acc[path] = {
+      types: `${path}/index.d.ts`,
+      import: `${path}/index.js`,
+      require: `${path}/${bundleName}.cjs`,
+    };
+    return acc;
+  }, {}),
+}
+
 // The root package.json points to the CJS/ESM source in "dist", to support
 // on-going package development (e.g. running tests, supporting npm link, etc.).
 // When publishing from "dist" however, we need to update the package.json