Fix for #2384 - fakes "sync" loading of web page by hiding it until styles are done

/ The actual XHR requests are changed to async for a speed boost for "sync" loading of orders of magnitude

lib/less-browser/bootstrap.js

@@ -3,7 +3,7 @@
  * used in the browser distributed version of less
  * to kick-start less using the browser api
  */
-/*global window */
+/*global window, document */
 
 // shim Promise if required
 require('promise/polyfill.js');
@@ -15,11 +15,31 @@ var less = module.exports = require("./index")(window, options);
 
 window.less = less;
 
+var css, head, style;
+
 if (options.onReady) {
     if (/!watch/.test(window.location.hash)) {
         less.watch();
     }
+    // Simulate synchronous stylesheet loading by blocking page rendering
+    if (!options.async) {
+        css = 'body { display: none !important }';
+        head = document.head || document.getElementsByTagName('head')[0];
+        style = document.createElement('style');
 
+        style.type = 'text/css';
+        if (style.styleSheet) {
+            style.styleSheet.cssText = css;
+        } else {
+            style.appendChild(document.createTextNode(css));
+        }
+
+        head.appendChild(style);
+    }
     less.registerStylesheetsImmediately();
-    less.pageLoadFinished = less.refresh(less.env === 'development');
+    less.pageLoadFinished = less.refresh(less.env === 'development').then(function() {
+        if (!options.async) {
+            head.removeChild(style);
+        }
+    });
 }

lib/less-browser/file-manager.js

@@ -39,7 +39,7 @@ module.exports = function(options, logger) {
     FileManager.prototype.doXHR = function doXHR(url, type, callback, errback) {
 
         var xhr = getXMLHttpRequest();
-        var async = options.isFileProtocol ? options.fileAsync : options.async;
+        var async = options.isFileProtocol ? options.fileAsync : true;
 
         if (typeof xhr.overrideMimeType === 'function') {
             xhr.overrideMimeType('text/css');