Only load Babel when needed. Closes #172

Author: Daniel15

src/React.Core/Babel.cs

@@ -243,7 +243,7 @@ protected virtual JavaScriptWithSourceMap TransformWithHeader(
 		/// <returns>JavaScript</returns>
 		public virtual string Transform(string input, string filename = "unknown")
 		{
-			EnsureBabelLoaded();
+			_environment.EnsureBabelLoaded();
 			try
 			{
 				var output = _environment.ExecuteWithLargerStackIfRequired<string>(
@@ -272,7 +272,7 @@ public virtual JavaScriptWithSourceMap TransformWithSourceMap(
 			string filename = "unknown"
 		)
 		{
-			EnsureBabelLoaded();
+			_environment.EnsureBabelLoaded();
 			try
 			{
 				return _environment.ExecuteWithLargerStackIfRequired<JavaScriptWithSourceMap>(
@@ -347,16 +347,5 @@ string filename
 			_fileSystem.WriteAsString(sourceMapPath, result.SourceMap == null ? string.Empty : result.SourceMap.ToJson());
 			return outputPath;
 		}
-
-		/// <summary>
-		/// Ensures that Babel has been loaded into the JavaScript engine.
-		/// </summary>
-		private void EnsureBabelLoaded()
-		{
-			if (!_config.LoadBabel)
-			{
-				throw new BabelNotLoadedException();
-			}
-		}
 	}
 }

src/React.Core/IReactEnvironment.cs

@@ -91,5 +91,10 @@ public interface IReactEnvironment
 		/// Gets the JSX Transformer for this environment.
 		/// </summary>
 		IBabel Babel { get; }
+
+		/// <summary>
+		/// Ensures that Babel has been loaded into the JavaScript engine.
+		/// </summary>
+		void EnsureBabelLoaded();
 	}
 }

src/React.Core/JavaScriptEngineFactory.cs

@@ -101,10 +101,6 @@ protected virtual void InitialiseEngine(IJsEngine engine)
 				engine.ExecuteResource("React.Resources.react-with-addons.js", thisAssembly);
 				engine.Execute("React = global.React");
 			}
-			if (_config.LoadBabel)
-			{
-				engine.ExecuteResource("React.node_modules.babel_core.browser.js", thisAssembly);
-			}
 
 			LoadUserScripts(engine);
 			if (!_config.LoadReact)

src/React.Core/ReactEnvironment.cs

@@ -413,5 +413,23 @@ public virtual IReactSiteConfiguration Configuration
 		{
 			get { return _config; }
 		}
+
+		/// <summary>
+		/// Ensures that Babel has been loaded into the JavaScript engine.
+		/// </summary>
+		public void EnsureBabelLoaded()
+		{
+			// If Babel is disabled in the config, don't even try loading it
+			if (!_config.LoadBabel)
+			{
+				throw new BabelNotLoadedException();
+			}
+
+			var babelLoaded = Engine.Evaluate<bool>("typeof global.Babel !== 'undefined'");
+			if (!babelLoaded)
+			{
+				Engine.ExecuteResource("React.node_modules.babel_core.browser.js", typeof(ReactEnvironment).Assembly);
+			}
+		}
 	}
 }