JS: Add watch support to copying flow files

js/build/copy-flow-files.js

@@ -1,14 +1,43 @@
 'use strict';
 
+const chokidar = require('chokidar');
 const fs = require('fs-extra');
-const glob = require('glob');
 const path = require('path');
 
-function exitIfError(err) {
+// Start at 1 for the initial scan.
+let pending = 1;
+
+const shouldWatch = process.argv.indexOf('-w') !== -1 ||
+                    process.argv.indexOf('--watch') !== -1;
+
+chokidar.watch('./src')
+    .on('add', copyFile)
+    .on('change', copyFile)
+    .on('unlink', removeFile)
+    .on('ready', done);
+
+function done(err) {
+  pending--;
   if (err) {
     console.error(err);  // eslint-disable-line
     process.exit(1);
   }
+  if (pending === 0 && !shouldWatch) {
+    process.exit(0);
+  }
+}
+
+function copyFile(f) {
+  pending++;
+  let nn = newName(f)
+  process.stdout.write(`${f} -> ${nn}\n`);
+  fs.copy(f, nn, {clobber: true}, done);
+}
+
+function removeFile(f) {
+  pending++;
+  process.stdout.write(`${f} -> /dev/null\n`);
+  fs.remove(f, done);
 }
 
 function newName(f) {
@@ -20,10 +49,3 @@ function newName(f) {
   parts[parts.length - 1] += '.flow';
   return parts.join(path.sep);
 }
-
-glob('src/**/*.js', (err, files) => {
-  exitIfError(err);
-  for (const f of files) {
-    fs.copy(f, newName(f), {clobber: true}, exitIfError);
-  }
-});

js/package.json

@@ -20,19 +20,18 @@
     "babel-preset-es2015": "^6.3.13",
     "babel-preset-react": "^6.3.13",
     "chai": "^3.2.0",
+    "chokidar": "^1.4.0",
     "eslint": "^1.9.0",
     "eslint-plugin-react": "^3.8.0",
     "flow-bin": "^0.19.1",
     "fs-extra": "^0.26.2",
-    "glob": "^6.0.1",
     "mocha": "^2.3.0"
   },
   "scripts": {
-    "build": "npm run copy-flow-files && BABEL_ENV=production babel src/ -d dist/",
-    "build-dev": "npm run copy-flow-files && babel src/ -d dist/",
+    "start": "node build/copy-flow-files.js -w & babel -w src/ -d dist/",
+    "build": "node build/copy-flow-files.js && BABEL_ENV=production babel src/ -d dist/",
     "pretest": "eslint src/ && flow src/",
-    "test": "mocha --ui tdd --reporter dot --require babel-polyfill --compilers js:babel-core/register src/",
-    "copy-flow-files": "node build/copy-flow-files.js"
+    "test": "mocha --ui tdd --reporter dot --require babel-polyfill --compilers js:babel-core/register src/"
   },
   "browser": {
     "./dist/fetch.js": "./dist/browser/fetch.js"