Fix to issue with async output and missing output directory

.babelrc

@@ -1,4 +1,17 @@
 {
-	"presets": ["es2015"],
-	"plugins": ["transform-flow-strip-types", "transform-object-rest-spread"]
+  "presets": [
+    ["env", {
+      "targets": {
+        "node": "6"
+      }
+    }]
+  ],
+  "plugins": [
+    ["transform-runtime", {
+      "polyfill": false,
+      "regenerator": true
+    }],
+    "transform-flow-strip-types",
+    "transform-object-rest-spread"
+  ]
 }

.flowconfig

@@ -0,0 +1,2 @@
+[ignore]
+	.*/node_modules/.*/node_modules/.*

README.md

@@ -187,9 +187,11 @@ Will output:
 
 The plugin takes a single object as its only parameter. The following properties are valid:
 
-| Arg          | Type      | Description                                 | Default                   |
-| ------------ | --------- | ------------------------------------------- | ------------------------- |
-| `outputPath` | `string`  | Path to which critical CSS should be output | Current working directory |
-| `outputDest` | `string`  | Default critical CSS file name              | `"critical.css"`          |
-| `preserve`   | `boolean` | Whether or not to remove selectors from primary CSS document once they've been marked as critical. This should prevent duplication of selectors across critical and non-critical CSS. | `true` |
-| `minify`     | `boolean` | Minify output CSS?                          | `true` |
+| Arg               | Type      | Description                                 | Default                   |
+| ----------------- | --------- | ------------------------------------------- | ------------------------- |
+| `outputPath`      | `string`  | Path to which critical CSS should be output | Current working directory |
+| `outputDest`      | `string`  | Default critical CSS file name              | `"critical.css"`          |
+| `preserve`        | `boolean` | Whether or not to remove selectors from primary CSS document once they've been marked as critical. This should prevent duplication of selectors across critical and non-critical CSS. | `true` |
+| `minify`          | `boolean` | Minify output CSS?                          | `true` |
+| `ignoreSelectors` | `array`   | Array of selectors to globally exclude from critical CSS output | `[]` |
+| `fsWriteRate`   | `number`  | Minimum amount of time between file writes, in millisenconds. This is intended to prevent overlapping file writes for codebases with numerous calls to `@critical` | `250` |

lib/atRule.js

@@ -4,7 +4,9 @@ Object.defineProperty(exports, "__esModule", {
   value: true
 });
 
-var _extends = Object.assign || function (target) { for (var i = 1; i < arguments.length; i++) { var source = arguments[i]; for (var key in source) { if (Object.prototype.hasOwnProperty.call(source, key)) { target[key] = source[key]; } } } return target; };
+var _extends2 = require('babel-runtime/helpers/extends');
+
+var _extends3 = _interopRequireDefault(_extends2);
 
 exports.getCriticalFromAtRule = getCriticalFromAtRule;
 
@@ -20,20 +22,20 @@ function _interopRequireDefault(obj) { return obj && obj.__esModule ? obj : { de
  * @param {Object} args Function args. See flow type alias.
  */
 function getCriticalFromAtRule(args) {
-  var result = {};
-  var options = _extends({
+  const result = {};
+  const options = (0, _extends3.default)({
     defaultDest: 'critical.css',
     css: _postcss2.default.root()
   }, args);
 
-  options.css.walkAtRules('critical', function (atRule) {
-    var name = atRule.params ? atRule.params : options.defaultDest;
+  options.css.walkAtRules('critical', atRule => {
+    const name = atRule.params ? atRule.params : options.defaultDest;
     // If rule has no nodes, all the nodes of the parent will be critical.
-    var rule = atRule;
+    let rule = atRule;
     if (!atRule.nodes) {
       rule = atRule.root();
     }
-    rule.clone().each(function (node) {
+    rule.clone().each(node => {
       if (node.name !== 'critical') {
         result[name] = result[name] ? result[name].append(node) : _postcss2.default.root().append(node);
       }

lib/getChildRules.js

@@ -21,23 +21,23 @@ function _interopRequireDefault(obj) { return obj && obj.__esModule ? obj : { de
  * @return {array} Array of child rules.
  */
 function getChildRules(css, parent) {
-  var result = [];
-  var selectorRegExp = new RegExp(parent.selector);
+  const result = [];
+  const selectorRegExp = new RegExp(parent.selector);
 
   // Walk all rules to mach child selectors
-  css.walkRules(selectorRegExp, function (rule) {
-    var childRule = (0, _matchChild.matchChild)(parent, rule);
+  css.walkRules(selectorRegExp, rule => {
+    const childRule = (0, _matchChild.matchChild)(parent, rule);
     if (childRule) {
       result.push(rule);
     }
   });
 
   // Walk all at-rules to match nested child selectors
-  css.walkAtRules(function (atRule) {
-    atRule.walkRules(selectorRegExp, function (rule) {
-      var childRule = (0, _matchChild.matchChild)(parent, rule);
+  css.walkAtRules(atRule => {
+    atRule.walkRules(selectorRegExp, rule => {
+      const childRule = (0, _matchChild.matchChild)(parent, rule);
       // Create new at-rule to append only necessary selector to critical
-      var criticalAtRule = _postcss2.default.atRule({
+      const criticalAtRule = _postcss2.default.atRule({
         name: atRule.name,
         params: atRule.params
       });
@@ -46,7 +46,7 @@ function getChildRules(css, parent) {
        * aren't identical.
        */
       if ((rule.selector === parent.selector || childRule) && _postcss2.default.parse(rule).toString() !== _postcss2.default.parse(parent).toString()) {
-        var clone = rule.clone();
+        const clone = rule.clone();
         criticalAtRule.append(clone);
         result.push(criticalAtRule);
       }

lib/getCriticalDestination.js

@@ -14,7 +14,7 @@ exports.getCriticalDestination = getCriticalDestination;
  * @return {string} String corresponding to output destination.
  */
 function getCriticalDestination(rule, dest) {
-  rule.walkDecls('critical-filename', function (decl) {
+  rule.walkDecls('critical-filename', decl => {
     dest = decl.value.replace(/['"]*/g, '');
     decl.remove();
   });

lib/getCriticalRules.js

@@ -24,14 +24,12 @@ function _interopRequireDefault(obj) { return obj && obj.__esModule ? obj : { de
  * @param {string} test Declaration string. Default  `critical-selector`
  * @return {Object} clone Cloned, cleaned root node.
  */
-function clean(root) {
-  var test = arguments.length > 1 && arguments[1] !== undefined ? arguments[1] : 'critical-selector';
-
-  var clone = root.clone();
+function clean(root, test = 'critical-selector') {
+  const clone = root.clone();
   if (clone.type === 'decl') {
     clone.remove();
   } else {
-    clone.walkDecls(test, function (decl) {
+    clone.walkDecls(test, decl => {
       decl.remove();
     });
   }
@@ -45,12 +43,12 @@ function clean(root) {
  * @return {Object} sortedRoot Root with nodes sorted by source order.
  */
 function correctSourceOrder(root) {
-  var sortedRoot = _postcss2.default.root();
-  var clone = root.clone();
-  clone.walkRules(function (rule) {
-    var start = rule.source.start.line;
+  const sortedRoot = _postcss2.default.root();
+  const clone = root.clone();
+  clone.walkRules(rule => {
+    let start = rule.source.start.line;
     if (rule.parent.type === 'atrule') {
-      var child = rule;
+      const child = rule;
       rule = _postcss2.default.atRule({
         name: rule.parent.name,
         params: rule.parent.params
@@ -91,11 +89,11 @@ function establishContainer(node) {
  * @return {Object} clonedRoot Root object.
  */
 function updateCritical(root, update) {
-  var clonedRoot = root.clone();
+  const clonedRoot = root.clone();
   if (update.type === 'rule') {
     clonedRoot.append(clean(update.clone()));
   } else {
-    update.clone().each(function (rule) {
+    update.clone().each(rule => {
       clonedRoot.append(clean(rule.root()));
     });
   }
@@ -111,21 +109,21 @@ function updateCritical(root, update) {
  * @return {object} Object containing critical rules, organized by output destination
  */
 function getCriticalRules(css, defaultDest) {
-  var critical = (0, _atRule.getCriticalFromAtRule)({ css: css, defaultDest: defaultDest });
-  css.walkDecls('critical-selector', function (decl) {
-    var parent = decl.parent,
-        value = decl.value;
-
-    var dest = (0, _getCriticalDestination.getCriticalDestination)(parent, defaultDest);
-    var container = establishContainer(parent);
-    var childRules = value === 'scope' ? (0, _getChildRules.getChildRules)(css, parent) : [];
+  const critical = (0, _atRule.getCriticalFromAtRule)({ css, defaultDest });
+  css.walkDecls('critical-selector', decl => {
+    const parent = decl.parent,
+          value = decl.value;
+
+    const dest = (0, _getCriticalDestination.getCriticalDestination)(parent, defaultDest);
+    const container = establishContainer(parent);
+    const childRules = value === 'scope' ? (0, _getChildRules.getChildRules)(css, parent) : [];
     // Sanity check, make sure we've got a root node
     critical[dest] = critical[dest] || _postcss2.default.root();
 
     switch (value) {
       case 'scope':
         // Add all child rules
-        var criticalRoot = childRules.reduce(function (acc, rule) {
+        const criticalRoot = childRules.reduce((acc, rule) => {
           return acc.append(rule.clone());
         }, critical[dest].append(container));