Add prettier script

`scripts/prettier/index.js write` will run prettier on source files.
Run using `yarn prettier`.

`scripts/prettier/index.js` will throw if any source files are not
formatted with prettier. We'll use this to block CI.

Based on similar script in Jest repo.

package.json

@@ -37,6 +37,7 @@
     "babylon": "6.15.0",
     "browserify": "^13.0.0",
     "bundle-collapser": "^1.1.1",
+    "chalk": "^1.1.3",
     "coffee-script": "^1.8.0",
     "core-js": "^2.2.1",
     "coveralls": "^2.11.6",
@@ -94,7 +95,7 @@
     "postinstall": "node node_modules/fbjs-scripts/node/check-dev-engines.js package.json",
     "test": "jest",
     "flow": "flow",
-    "prettier": "prettier --write --no-bracket-spacing --single-quote --jsx-bracket-same-line --trailing-comma all --print-width 80 \"src/**/!(third_party)/*.js\""
+    "prettier": "node ./scripts/prettier/index.js write"
   },
   "jest": {
     "modulePathIgnorePatterns": [

scripts/prettier/index.js

@@ -0,0 +1,70 @@
+/**
+ * Copyright (c) 2014-present, Facebook, Inc. All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+'use strict';
+
+// Based on similar script in Jest
+// https://github.com/facebook/jest/blob/master/scripts/prettier.js
+
+const chalk = require('chalk');
+const glob = require('glob');
+const path = require('path');
+const runCommand = require('./runCommand');
+
+const shouldWrite = process.argv[2] === 'write';
+const isWindows = process.platform === 'win32';
+const prettier = isWindows ? 'prettier.cmd' : 'prettier';
+const prettierCmd = path.resolve(__dirname, '../../node_modules/.bin/' + prettier);
+const defaultOptions = {
+  'bracket-spacing': 'false',
+  'single-quote': 'true',
+  'jsx-bracket-same-line': 'true',
+  'trailing-comma': 'all',
+  'print-width': 80,
+};
+const config = {
+  default: {
+    patterns: ['src/**/*.js'],
+    ignore: [
+      '**/third_party/**',
+      '**/node_modules/**',
+    ],
+  },
+};
+
+Object.keys(config).forEach(key => {
+  const patterns = config[key].patterns;
+  const options = config[key].options;
+  const ignore = config[key].ignore;
+
+  const globPattern = patterns.length > 1
+    ? `{${patterns.join(',')}}`
+    : `${patterns.join(',')}`;
+  const files = glob.sync(globPattern, {ignore});
+
+  const args = Object.keys(defaultOptions).map(
+    k => `--${k}=${(options && options[k]) || defaultOptions[k]}`
+  );
+  args.push(`--${shouldWrite ? 'write' : 'l'} {${files.join(' ')}}`);
+
+  try {
+    runCommand(prettierCmd, args.join(' '), path.resolve(__dirname, '../..'));
+  } catch (e) {
+    console.log(e);
+    if (!shouldWrite) {
+      console.log(
+        chalk.red(
+          `  This project uses prettier to format all JavaScript code.\n`
+        ) +
+          chalk.dim(`    Please run `) +
+          chalk.reset('yarn prettier') +
+          chalk.dim(` and add changes to files listed above to your commit.`) +
+          `\n`
+      );
+    }
+  }
+});

scripts/prettier/runCommand.js

@@ -0,0 +1,40 @@
+/**
+ * Copyright (c) 2014, Facebook, Inc. All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+'use strict';
+
+const chalk = require('chalk');
+const spawn = require('child_process').spawnSync;
+
+module.exports = function runCommand(cmd, args, cwd) {
+  if (!cwd) {
+    cwd = __dirname;
+  }
+
+  const callArgs = args.split(' ');
+  console.log(
+    chalk.dim('$ cd ' + cwd) +
+      '\n' +
+      chalk.dim(
+        '  $ ' +
+          cmd +
+          ' ' +
+          (args.length > 1000 ? args.slice(0, 1000) + '...' : args)
+      ) +
+      '\n'
+  );
+  const result = spawn(cmd, callArgs, {
+    cwd,
+    stdio: 'inherit',
+  });
+  if (result.error || result.status !== 0) {
+    const message = 'Error running command.';
+    const error = new Error(message);
+    error.stack = message;
+    throw error;
+  }
+};