Store list of available JavaScript engine factories in static variable

Author: Daniel15

src/React/AssemblyRegistration.cs

@@ -7,6 +7,9 @@
  *  of patent rights can be found in the PATENTS file in the same directory.
  */
 
+using JavaScriptEngineSwitcher.Jint;
+using JavaScriptEngineSwitcher.Msie;
+using JavaScriptEngineSwitcher.Msie.Configuration;
 using React.TinyIoC;
 
 namespace React
@@ -37,6 +40,20 @@ public void Register(TinyIoCContainer container)
 
 			container.Register<IReactEnvironment, ReactEnvironment>().AsPerRequestSingleton();
 			container.Register<IJavaScriptEngineFactory, JavaScriptEngineFactory>().AsPerRequestSingleton();
+
+			// JavaScript engines
+			JavaScriptEngineFactory.AddFactoryWithPriority(
+				() => new MsieJsEngine(new MsieConfiguration { EngineMode = JsEngineMode.ChakraActiveScript }),
+				priority: 10
+			);
+			JavaScriptEngineFactory.AddFactoryWithPriority(
+				() => new MsieJsEngine(new MsieConfiguration { EngineMode = JsEngineMode.Classic }),
+				priority: 20
+			);
+			JavaScriptEngineFactory.AddFactoryWithPriority(
+				() => new JintJsEngine(),
+				priority: 100
+			);
 		}
 	}
 }

src/React/JavaScriptEngineFactory.cs

@@ -2,11 +2,9 @@
 using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Linq;
 using System.Threading;
 using JavaScriptEngineSwitcher.Core;
-using JavaScriptEngineSwitcher.Jint;
-using JavaScriptEngineSwitcher.Msie;
-using JavaScriptEngineSwitcher.Msie.Configuration;
 using React.Exceptions;
 
 namespace React
@@ -17,6 +15,11 @@ namespace React
 	public class JavaScriptEngineFactory : IDisposable, IJavaScriptEngineFactory
 	{
 		/// <summary>
+		/// List of all available JavaScript engines
+		/// </summary>
+		private static readonly IList<FactoryWithPriority> _availableFactories
+			= new List<FactoryWithPriority>();
+		/// <summary>
 		/// Function used to create new JavaScript engine instances.
 		/// </summary>
 		private readonly Func<IJsEngine> _factory; 
@@ -34,6 +37,25 @@ public JavaScriptEngineFactory()
 			_factory = GetFactory();
 		}
 
+		/// <summary>
+		/// Adds a supported JavaScript engine. When an instance of 
+		/// <see cref="JavaScriptEngineFactory" /> is created, the first functioning JavaScript 
+		/// engine with the lowest priority will be used.
+		/// </summary>
+		/// <param name="factory">Factory method to create new instance of the engine</param>
+		/// <param name="priority">
+		/// Any number. All engines will be sorted by priority, so "better" engines should have
+		/// a lower priority number.
+		/// </param>
+		public static void AddFactoryWithPriority(Func<IJsEngine> factory, int priority)
+		{
+			_availableFactories.Add(new FactoryWithPriority
+			{
+				Factory = factory,
+				Priority = priority
+			});
+		}
+
 		/// <summary>
 		/// Gets the JavaScript engine for the current thread
 		/// </summary>
@@ -76,12 +98,9 @@ public void DisposeEngineForCurrentThread()
 		/// <returns>Function to create JavaScript engine</returns>
 		private static Func<IJsEngine> GetFactory()
 		{
-			var availableEngineFactories = new List<Func<IJsEngine>>
-			{
-				() => new MsieJsEngine(new MsieConfiguration { EngineMode = JsEngineMode.ChakraActiveScript }),
-				() => new MsieJsEngine(new MsieConfiguration { EngineMode = JsEngineMode.Classic }),
-				() => new JintJsEngine()
-			};
+			var availableEngineFactories = _availableFactories
+				.OrderBy(x => x.Priority)
+				.Select(x => x.Factory);
 			foreach (var engineFactory in availableEngineFactories)
 			{
 				IJsEngine engine = null;
@@ -126,5 +145,11 @@ public void Dispose()
 				}
 			}
 		}
+
+		private class FactoryWithPriority
+		{
+			public Func<IJsEngine> Factory { get; set; }
+			public int Priority { get; set; }
+		}
 	}
 }