Expose the initial context via @root

lib/handlebars/compiler/javascript-compiler.js

@@ -121,7 +121,7 @@ JavaScriptCompiler.prototype = {
 
       var copies = "helpers = this.merge(helpers, " + namespace + ".helpers);";
       if (this.environment.usePartial) { copies = copies + " partials = this.merge(partials, " + namespace + ".partials);"; }
-      if (this.options.data) { copies = copies + " data = data || {};"; }
+      if (this.options.data) { copies = copies + " data = this.initData(depth0, data);"; }
       out.push(copies);
     } else {
       out.push('');

lib/handlebars/runtime.js

@@ -1,6 +1,6 @@
 module Utils from "./utils";
 import Exception from "./exception";
-import { COMPILER_REVISION, REVISION_CHANGES } from "./base";
+import { COMPILER_REVISION, REVISION_CHANGES, createFrame } from "./base";
 
 export function checkRevision(compilerInfo) {
   var compilerRevision = compilerInfo && compilerInfo[0] || 1,
@@ -56,6 +56,13 @@ export function template(templateSpec, env) {
       }
       return programWrapper;
     },
+    initData: function(context, data) {
+      data = data ? createFrame(data) : {};
+      if (!('root' in data)) {
+        data.root = context;
+      }
+      return data;
+    },
     merge: function(param, common) {
       var ret = param || common;