AngleSharp · FlorianRappl · Jul 26, 2026 · Jul 26, 2026
diff --git a/src/AngleSharp.Js.Tests/InteractionTests.cs b/src/AngleSharp.Js.Tests/InteractionTests.cs
@@ -113,6 +113,30 @@ public async Task RunScriptSnippetDirectlyGetSimpleValueFromCalculation()
             Assert.AreEqual(3.0, result);
         }
 
+        [Test]
+        public async Task RunSameScriptSourceInSeveralDocumentsKeepsStateSeparate()
+        {
+            var html = "<!doctype html><span id=test>Test</span>";
+            var config = Configuration.Default.WithJs();
+            var source = "(function () { window.counter = (window.counter || 0) + 1; return window.counter; })()";
+            var first = await BrowsingContext.New(config).OpenAsync(m => m.Content(html));
+            var second = await BrowsingContext.New(config).OpenAsync(m => m.Content(html));
+
+            Assert.AreEqual(1.0, first.ExecuteScript(source));
+            Assert.AreEqual(1.0, second.ExecuteScript(source));
+            Assert.AreEqual(2.0, first.ExecuteScript(source));
+            Assert.AreEqual(2.0, second.ExecuteScript(source));
+        }
+
+        [Test]
+        public async Task RunScriptSnippetWithSyntaxErrorThrows()
+        {
+            var html = "<!doctype html><span id=test>Test</span>";
+            var config = Configuration.Default.WithJs();
+            var document = await BrowsingContext.New(config).OpenAsync(m => m.Content(html));
+            Assert.Throws<JavaScriptException>(() => document.ExecuteScript("function ("));
+        }
+
         [Test]
         public async Task RunScriptAtPressingLink_Issue47()
         {

diff --git a/src/AngleSharp.Js/Cache/ScriptCache.cs b/src/AngleSharp.Js/Cache/ScriptCache.cs
@@ -0,0 +1,54 @@
+namespace AngleSharp.Js.Cache
+{
+    using Acornima.Ast;
+    using Jint;
+    using Jint.Runtime;
+    using System;
+    using System.Collections.Concurrent;
+
+    /// <summary>
+    /// Caches the parsed and analyzed form of scripts. A prepared script is
+    /// documented by Jint as reusable and thread-safe, so the same one can serve
+    /// every document that runs the same source - a page loading a library ends up
+    /// parsing it once instead of once per document.
+    /// </summary>
+    static class ScriptCache
+    {
+        //  There is no bound on how many distinct scripts a process may see, so the
+        //  cache does not grow without end. The scripts worth keeping are the ones
+        //  seen first: libraries are referenced early and by many documents.
+        private const Int32 Capacity = 32;
+
+        private static readonly ConcurrentDictionary<String, Prepared<Script>> _scripts =
+            new ConcurrentDictionary<String, Prepared<Script>>(StringComparer.Ordinal);
+
+        /// <summary>
+        /// Gets the prepared form of the given source. An invalid result means the
+        /// source could not be prepared and should be handed to the engine as text,
+        /// so that the engine reports the syntax error itself.
+        /// </summary>
+        public static Prepared<Script> GetOrCreate(String source)
+        {
+            if (_scripts.TryGetValue(source, out var prepared))
+            {
+                return prepared;
+            }
+
+            try
+            {
+                prepared = Engine.PrepareScript(source);
+            }
+            catch (ScriptPreparationException)
+            {
+                return default;
+            }
+
+            if (_scripts.Count < Capacity)
+            {
+                _scripts.TryAdd(source, prepared);
+            }
+
+            return prepared;
+        }
+    }
+}
diff --git a/src/AngleSharp.Js/EngineInstance.cs b/src/AngleSharp.Js/EngineInstance.cs
@@ -2,6 +2,7 @@ namespace AngleSharp.Js
 {
     using AngleSharp.Dom;
     using AngleSharp.Io;
+    using AngleSharp.Js.Cache;
     using AngleSharp.Text;
     using Jint;
     using Jint.Native;
@@ -84,7 +85,7 @@ public EngineInstance(IWindow window, IDictionary<String, Object> assignments, I
 
         public ObjectInstance GetDomPrototype(Type type) => _prototypes.GetOrCreate(type, CreatePrototype);
 
-        public JsValue RunScript(String source, String type, String sourceUrl, JsValue context)
+        public JsValue RunScript(String source, String type, String sourceUrl)
         {
             if (string.IsNullOrEmpty(type))
             {
@@ -95,7 +96,10 @@ public JsValue RunScript(String source, String type, String sourceUrl, JsValue c
             {
                 if (MimeTypeNames.IsJavaScript(type))
                 {
-                    return _engine.Evaluate(source);
+                    var prepared = ScriptCache.GetOrCreate(source);
+                    //  An invalid result means the source did not parse; hand it to the
+                    //  engine as text so the syntax error is reported as usual.
+                    return prepared.IsValid ? _engine.Evaluate(prepared) : _engine.Evaluate(source);
                 }
                 else if (type.Isi("importmap"))
                 {

diff --git a/src/AngleSharp.Js/Extensions/EngineExtensions.cs b/src/AngleSharp.Js/Extensions/EngineExtensions.cs
@@ -209,12 +209,6 @@ public static void AddInstance(this EngineInstance engine, ObjectInstance obj, T
             apply.Invoke(engine, obj);
         }
 
-        public static JsValue RunScript(this EngineInstance engine, String source, String type, String sourceUrl) =>
-            engine.RunScript(source, type, sourceUrl, engine.Window);
-
-        public static JsValue RunScript(this EngineInstance engine, String source, String type, String sourceUrl, INode context) =>
-            engine.RunScript(source, type, sourceUrl, context.ToJsValue(engine));
-
         public static JsValue Call(this EngineInstance instance, MethodInfo method, JsValue thisObject, JsValue[] arguments)
         {
             if (method != null)