Fix string.split and array.join performance

Jint.Benchmark/DromaeoBenchmark.cs

@@ -0,0 +1,74 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using BenchmarkDotNet.Attributes;
+using BenchmarkDotNet.Configs;
+using BenchmarkDotNet.Jobs;
+using Jint;
+
+namespace Esprima.Benchmark
+{
+    [Config(typeof(Config))]
+    [MemoryDiagnoser]
+    public class DromaeoBenchmark
+    {
+        private class Config : ManualConfig
+        {
+            public Config()
+            {
+                // if Jint array performance gets better we can go towards defaul 16/16
+                Add(Job.ShortRun.WithInvocationCount(4).WithUnrollFactor(4));
+            }
+        }
+
+        private static readonly Dictionary<string, string> files = new Dictionary<string, string>
+        {
+            {"dromaeo-3d-cube", null},
+            {"dromaeo-core-eval", null},
+            {"dromaeo-object-array", null},
+            {"dromaeo-object-regexp", null},
+            {"dromaeo-object-string", null},
+            {"dromaeo-string-base64", null}
+        };
+
+        private Engine engine;
+
+        [GlobalSetup]
+        public void Setup()
+        {
+            foreach (var fileName in files.Keys.ToList())
+            {
+                files[fileName] = File.ReadAllText($"Scripts/dromaeo/{fileName}.js");
+            }
+
+            engine = new Engine()
+                .SetValue("log", new Action<object>(Console.WriteLine))
+                .SetValue("assert", new Action<bool>(b => { }));
+
+            engine.Execute(@"
+var startTest = function () { };
+var test = function (name, fn) { fn(); };
+var endTest = function () { };
+var prep = function (fn) { fn(); };
+");
+        }
+
+        [ParamsSource(nameof(FileNames))]
+        public string FileName { get; set; }
+
+        public IEnumerable<string> FileNames()
+        {
+            foreach (var entry in files)
+            {
+                yield return entry.Key;
+            }
+        }
+
+        [Benchmark]
+        public void Run()
+        {
+            engine.Execute(files[FileName]);
+        }
+    }
+}

Jint.Benchmark/Jint.Benchmark.csproj

@@ -14,6 +14,7 @@
     <GenerateAssemblyFileVersionAttribute>false</GenerateAssemblyFileVersionAttribute>
   </PropertyGroup>
   <ItemGroup>
+    <None Include=".\Scripts\**" CopyToOutputDirectory="PreserveNewest" />
     <None Include="..\Jint.Tests.CommonScripts\Scripts\**" CopyToOutputDirectory="PreserveNewest" LinkBase="SunSpider" />
   </ItemGroup>
   <ItemGroup>