module: development and production exports conditions

doc/api/esm.md

@@ -358,6 +358,9 @@ Node.js supports the following conditions:
 * `"node"` - matched for any Node.js environment. Can be a CommonJS or ES
    module file. _This condition should always come after `"import"` or
    `"require"`._
+* `"production"` - matched if `process.env.NODE_ENV` is set to `production`.
+* `"development"` - matched if `process.env.NODE_ENV` is not set to `production`
+   so that `"production"` and `"development"` are fully mutually exclusive.
 * `"default"` - the generic fallback that will always match. Can be a CommonJS
    or ES module file. _This condition should always come last._
 
@@ -383,6 +386,10 @@ Conditional exports can also be extended to exports subpaths, for example:
   "exports": {
     ".": "./main.js",
     "./feature": {
+      "production": {
+        "browser": "./feature-browser-production.js",
+        "default": "./feature-production.js"
+      },
       "browser": "./feature-browser.js",
       "default": "./feature.js"
     }
@@ -391,8 +398,9 @@ Conditional exports can also be extended to exports subpaths, for example:
 ```
 
 Defines a package where `require('pkg/feature')` and `import 'pkg/feature'`
-could provide different implementations between the browser and Node.js,
-given third-party tool support for a `"browser"` condition.
+could provide different implementations between the browser and Node.js
+given third-party tool support for a `"browser"` condition, while also
+supporting production and development variants.
 
 #### Nested conditions
 
@@ -1472,7 +1480,9 @@ In the following algorithms, all subroutine errors are propagated as errors
 of these top-level routines unless stated otherwise.
 
 _defaultEnv_ is the conditional environment name priority array,
-`["node", "import"]`.
+`["node", "import", "development"]`. If `process.env.NODE_ENV` is set to
+`production` then the `"production"` condition is used in place of
+`"development"`.
 
 The resolver can throw the following errors:
 * _Invalid Module Specifier_: Module specifier is an invalid URL, package name

lib/internal/modules/cjs/loader.js

@@ -524,6 +524,8 @@ function isArrayIndex(p) {
   return n >= 0 && n < (2 ** 32) - 1;
 }
 
+const devCondition =
+    process.env.NODE_ENV === 'production' ? 'production' : 'development';
 function resolveExportsTarget(baseUrl, target, subpath, mappingKey) {
   if (typeof target === 'string') {
     let resolvedTarget, resolvedTargetPath;
@@ -575,6 +577,14 @@ function resolveExportsTarget(baseUrl, target, subpath, mappingKey) {
     }
     for (const p of keys) {
       switch (p) {
+        case devCondition:
+          try {
+            return resolveExportsTarget(baseUrl, target[p], subpath,
+                                        mappingKey);
+          } catch (e) {
+            if (e.code !== 'ERR_PACKAGE_PATH_NOT_EXPORTED') throw e;
+          }
+          break;
         case 'node':
         case 'require':
           try {

lib/internal/modules/esm/resolve.js

@@ -46,7 +46,11 @@ const {
   ERR_UNSUPPORTED_ESM_URL_SCHEME,
 } = require('internal/errors').codes;
 
-const DEFAULT_CONDITIONS = ObjectFreeze(['node', 'import']);
+const DEFAULT_CONDITIONS = ObjectFreeze([
+  'node',
+  'import',
+  process.env.NODE_ENV === 'production' ? 'production' : 'development'
+]);
 const DEFAULT_CONDITIONS_SET = new SafeSet(DEFAULT_CONDITIONS);
 
 function getConditionsSet(conditions) {

test/es-module/test-esm-exports-dev-production.mjs

@@ -0,0 +1,27 @@
+// Flags: --experimental-wasm-modules
+import '../common/index.mjs';
+import { path } from '../common/fixtures.mjs';
+import { strictEqual } from 'assert';
+import { spawnSync } from 'child_process';
+
+{
+  const output = spawnSync(process.execPath, [path('/pkgexports-dev.mjs')], {
+    env: Object.assign({}, process.env, {
+      NODE_ENV: 'production'
+    })
+  });
+  strictEqual(output.stdout.toString().trim(), 'production');
+}
+
+{
+  const output = spawnSync(process.execPath, [path('/pkgexports-dev.mjs')], {
+  });
+  strictEqual(output.stdout.toString().trim(), 'development');
+}
+
+{
+  const output = spawnSync(process.execPath, [path('/pkgexports-dev.mjs')], {
+    NODE_ENV: 'any'
+  });
+  strictEqual(output.stdout.toString().trim(), 'development');
+}

test/fixtures/es-module-loaders/loader-with-custom-condition.mjs

@@ -1,8 +1,11 @@
 import {ok, deepStrictEqual} from 'assert';
 
+const env =
+    process.env.NODE_ENV === 'production' ? 'production' : 'development';
+
 export async function resolve(specifier, context, defaultResolve) {
   ok(Array.isArray(context.conditions), 'loader receives conditions array');
-  deepStrictEqual([...context.conditions].sort(), ['import', 'node']);
+  deepStrictEqual([...context.conditions].sort(), [env, 'import', 'node']);
   return defaultResolve(specifier, {
     ...context,
     conditions: ['custom-condition', ...context.conditions],

test/fixtures/pkgexports-dev.mjs

@@ -0,0 +1,17 @@
+import { fileURLToPath } from 'url';
+import { createRequire } from 'module';
+import { strictEqual } from 'assert';
+
+const require = createRequire(fileURLToPath(import.meta.url));
+
+const production = process.env.NODE_ENV === 'production';
+const expectValue = production ? 'production' : 'development';
+
+strictEqual(require('pkgexports-dev'), expectValue);
+
+(async () => {
+  const { default: value } = await import('pkgexports-dev');
+  strictEqual(value, expectValue);
+
+  console.log(expectValue);
+})();