fix(node-resolve): fix "browser" and "exports.browser" field mappings

packages/node-resolve/rollup.config.js

@@ -12,7 +12,7 @@ export default {
     throw new Error(warning);
   },
   output: [
-    { file: pkg.main, format: 'cjs', exports: 'named' },
+    { file: pkg.main, format: 'cjs', exports: 'named', sourcemap: true },
     { file: pkg.module, format: 'es', plugins: [emitModulePackageFile()] }
   ]
 };

packages/node-resolve/src/package/resolvePackageTarget.js

@@ -86,10 +86,25 @@ async function resolvePackageTarget(context, { target, subpath, pattern, interna
   }
 
   if (target && typeof target === 'object') {
+    const { packageBrowserField, useBrowserOverrides } = context;
+    let browserTarget = null;
+
+    if (useBrowserOverrides) {
+      if (Object.keys(target).includes('browser')) {
+        browserTarget = target.browser;
+      } else {
+        for (const [, value] of Object.entries(target)) {
+          if (packageBrowserField[value]) {
+            browserTarget = value;
+          }
+        }
+      }
+    }
+
     for (const [key, value] of Object.entries(target)) {
       if (key === 'default' || context.conditions.includes(key)) {
         const resolved = await resolvePackageTarget(context, {
-          target: value,
+          target: browserTarget || value,
           subpath,
           pattern,
           internal

packages/node-resolve/src/resolveImportSpecifiers.js

@@ -92,6 +92,8 @@ async function resolveId({
       importer,
       moduleDirs: moduleDirectories,
       conditions: exportConditions,
+      useBrowserOverrides,
+      packageBrowserField,
       resolveId(id, parent) {
         return resolveId({
           importSpecifier: id,
@@ -103,6 +105,7 @@ async function resolveId({
           mainFields,
           preserveSymlinks,
           useBrowserOverrides,
+          packageBrowserField,
           baseDir,
           moduleDirectories
         });
@@ -127,7 +130,9 @@ async function resolveId({
           moduleDirs: moduleDirectories,
           pkgURL,
           pkgJsonPath,
-          conditions: exportConditions
+          conditions: exportConditions,
+          useBrowserOverrides,
+          packageBrowserField
         };
         const resolvedPackageExport = await resolvePackageExports(
           context,

packages/node-resolve/test/browser.js

@@ -199,3 +199,33 @@ test('pkg.browser with mapping to prevent bundle by specifying a value of false'
 
   t.is(module.exports, 'ok');
 });
+
+test('pkg.browser can override the export map result', async (t) => {
+  const bundle = await rollup({
+    input: 'browser-override-exports.js',
+    plugins: [nodeResolve({ browser: true }), commonjs()]
+  });
+  const { module } = await testBundle(t, bundle);
+
+  t.is(module.exports, 'browser');
+});
+
+test('exports.browser takes precedence over export map result, when browser:true', async (t) => {
+  const bundle = await rollup({
+    input: 'browser-exports-browser.js',
+    plugins: [nodeResolve({ browser: true }), commonjs()]
+  });
+  const { module } = await testBundle(t, bundle);
+
+  t.is(module.exports, 'browser');
+});
+
+test('exports.browser does not take precedence over export map result, when browser:false', async (t) => {
+  const bundle = await rollup({
+    input: 'browser-exports-browser.js',
+    plugins: [nodeResolve(), commonjs()]
+  });
+  const { module } = await testBundle(t, bundle);
+
+  t.is(module.exports, 'require');
+});

packages/node-resolve/test/fixtures/browser-exports-browser.js

@@ -0,0 +1,3 @@
+const b = require('exports-browser');
+
+module.exports = b;

packages/node-resolve/test/fixtures/browser-override-exports.js

@@ -0,0 +1,3 @@
+const Nanoid = require('nanoid');
+
+module.exports = Nanoid;