Add support for ES modules

Closes GH-13.

lib/generate/config.js

@@ -18,6 +18,7 @@ function config(ctx) {
     main = resolveFrom(mainRoot, mainId)
   } catch (error) {}
 
+  ctx.experimentalModules = settings.experimentalModules || false
   ctx.cwd = cwd
   ctx.main = main
   ctx.name = settings.name || pkg.name || null

lib/generate/instrument.js

@@ -39,6 +39,9 @@ function instrument(ctx, next) {
 
     return {
       visitor: {
+        ImportDeclaration: function(path) {
+          instrumentMainReference(path.node.source)
+        },
         CallExpression: function(path) {
           var callee = path.get('callee')
 

lib/generate/run.js

@@ -5,7 +5,15 @@ var exec = require('child_process').exec
 module.exports = run
 
 function run(ctx, next) {
-  exec('node ' + ctx.exampleInstrumentedPath, onexec)
+  var cmd = [process.execPath]
+
+  if (ctx.experimentalModules) {
+    cmd.push('--experimental-modules')
+  }
+
+  cmd.push(ctx.exampleInstrumentedPath)
+
+  exec(cmd.join(' '), onexec)
 
   function onexec(err, stdout) {
     var logs = ctx.logs

lib/generate/write.js

@@ -7,7 +7,8 @@ module.exports = write
 
 function write(ctx, next) {
   var dir = path.dirname(ctx.examplePath)
-  var filePath = path.join(dir, ctx.id + '.js')
+  var extname = path.extname(ctx.examplePath)
+  var filePath = path.join(dir, ctx.id + extname)
 
   fs.writeFile(filePath, ctx.exampleInstrumented, onwrite)
 

readme.md

@@ -153,6 +153,13 @@ If given, resolved from [`file.cwd`][file-cwd].
 If inferred from `package.json`, resolved relating to that package root.
 Used to rewrite `require('.')` to `require('name')`.
 
+###### `options.experimentalModules`
+
+Pass [`--experimental-modules`][experimental-modules] when running the example
+in Node.
+This lets you use ECMAScript Modules if the current version of Node does support
+this flag, but *does not* support ES modules natively.
+
 ## Contribute
 
 See [`contributing.md`][contributing] in [`remarkjs/.github`][health] for ways
@@ -213,6 +220,8 @@ abide by its terms.
 
 [file-cwd]: https://github.com/vfile/vfile#vfilecwd
 
+[experimental-modules]: https://nodejs.org/api/esm.html
+
 [usage]: #use
 
 [example-js]: example.js

test/fixtures/es-module-mjs/config.json

@@ -0,0 +1,3 @@
+{
+  "experimentalModules": true
+}

test/fixtures/es-module-mjs/example.mjs

@@ -0,0 +1,4 @@
+import { pi } from "./index.mjs";
+
+// `pi` yields:
+console.log('text', pi)

test/fixtures/es-module-mjs/index.mjs

@@ -0,0 +1 @@
+export const pi = Math.floor(Math.PI * 1e6) / 1e6

test/fixtures/es-module-mjs/output.md

@@ -0,0 +1,13 @@
+# PI
+
+## Usage
+
+```javascript
+import { pi } from "pi";
+```
+
+`pi` yields:
+
+```text
+3.141592
+```

test/fixtures/es-module-mjs/package.json

@@ -0,0 +1,3 @@
+{
+  "name": "pi"
+}

test/fixtures/es-module-mjs/readme.md

@@ -0,0 +1,3 @@
+# PI
+
+## Usage

test/fixtures/es-module-type-module/config.json

@@ -0,0 +1,3 @@
+{
+  "experimentalModules": true
+}

test/fixtures/es-module-type-module/example.js

@@ -0,0 +1,4 @@
+import { pi } from "./index.js";
+
+// `pi` yields:
+console.log('text', pi)

test/fixtures/es-module-type-module/index.js

@@ -0,0 +1 @@
+export const pi = Math.floor(Math.PI * 1e6) / 1e6

test/fixtures/es-module-type-module/output.md

@@ -0,0 +1,13 @@
+# PI
+
+## Usage
+
+```javascript
+import { pi } from "pi";
+```
+
+`pi` yields:
+
+```text
+3.141592
+```

test/fixtures/es-module-type-module/package.json

@@ -0,0 +1,4 @@
+{
+  "name": "pi",
+  "type": "module"
+}

test/fixtures/es-module-type-module/readme.md

@@ -0,0 +1,3 @@
+# PI
+
+## Usage