feat: support esm (#1474)

.gitignore

@@ -4,3 +4,4 @@ coverage
 npm-debug.log
 .idea
 *.iml
+dist

.travis.yml

@@ -3,6 +3,7 @@ node_js:
   - 8
   - 10
   - 12
+  - 14
 cache:
   directories:
     - wrk/bin
@@ -13,6 +14,7 @@ before_script:
   - export PATH=$PATH:$PWD/wrk/bin/
 script:
   - npm run lint
+  - npm run prepack
   - npm run test-cov
   - npm run bench
 after_script:

package.json

@@ -3,12 +3,21 @@
   "version": "2.12.1",
   "description": "Koa web app framework",
   "main": "lib/application.js",
+  "exports": {
+    ".": {
+      "require": "./lib/application.js",
+      "import": "./dist/koa.mjs"
+    },
+    "./": "./"
+  },
   "scripts": {
     "test": "egg-bin test test",
     "test-cov": "egg-bin cov test",
     "lint": "eslint benchmarks lib test",
     "bench": "make -C benchmarks",
-    "authors": "git log --format='%aN <%aE>' | sort -u > AUTHORS"
+    "authors": "git log --format='%aN <%aE>' | sort -u > AUTHORS",
+    "build": "gen-esm-wrapper . ./dist/koa.mjs",
+    "prepack": "npm run build"
   },
   "repository": "koajs/koa",
   "keywords": [
@@ -55,13 +64,15 @@
     "eslint-plugin-node": "^10.0.0",
     "eslint-plugin-promise": "^4.2.1",
     "eslint-plugin-standard": "^4.0.1",
+    "gen-esm-wrapper": "^1.0.6",
     "mm": "^2.5.0",
     "supertest": "^3.1.0"
   },
   "engines": {
     "node": "^4.8.4 || ^6.10.1 || ^7.10.1 || >= 8.1.4"
   },
   "files": [
+    "dist",
     "lib"
   ]
 }

test/load-with-esm.js

@@ -0,0 +1,36 @@
+const assert = require('assert');
+
+let importESM = () => {};
+
+describe('Load with esm', () => {
+  before(function(){
+    // ESM support is flagged on v12.x.
+    const majorVersion = +process.version.split('.')[0].slice(1);
+    if (majorVersion < 12) {
+      this.skip();
+    } else {
+      // eslint-disable-next-line no-eval
+      importESM = eval('(specifier) => import(specifier)');
+    }
+  });
+
+  it('should default export koa', async() => {
+    const exported = await importESM('koa');
+    const required = require('../');
+    assert.strictEqual(exported.default, required);
+  });
+
+  it('should match exports own property names', async() => {
+    const exported = new Set(Object.getOwnPropertyNames(await importESM('koa')));
+    const required = new Set(Object.getOwnPropertyNames(require('../')));
+
+    // Remove constructor properties + default export.
+    for (const k of ['prototype', 'length', 'name']) {
+      required.delete(k);
+    }
+    exported.delete('default');
+
+    assert.strictEqual(exported.size, required.size);
+    assert.strictEqual([...exported].every(property => required.has(property)), true);
+  });
+});