Jint

CLR interop ​

SetValue projects CLR primitives, delegates, objects, collections, and types into JavaScript.

csharp
var person = new Person { Name = "Ada" };

var engine = new Engine()
    .SetValue("person", person)
    .SetValue("write", new Action<string>(Console.WriteLine));

engine.Execute("write(person.Name)");

Public properties and methods are available through the wrapper. Direct writes to CLR properties, fields, indexers, dictionaries, lists, and live arrays are disabled by default:

csharp
var engine = new Engine(options => options.Interop.AllowWrite = true)
    .SetValue("person", person);

engine.Execute("'use strict'; person.Name = 'Grace'");

AllowWrite does not make objects safe when false. Methods, delegates, and registered extension methods can still mutate host state. Expose only intended capabilities to untrusted scripts.

CLR namespaces and types ​

Namespace access is disabled by default. Prefer exporting individual values or types. If namespace lookup is required, allow only the needed assemblies:

csharp
var engine = new Engine(options =>
    options.AllowClr(typeof(MyPublicApi).Assembly));

An explicit type can be exported without enabling namespace lookup:

csharp
engine.SetValue(
    "MyPublicApi",
    TypeReference.CreateTypeReference<MyPublicApi>(engine));

An assembly allowlist is not a complete sandbox. An allowed API may load assemblies, access files or networks, start processes, or return more powerful objects. For untrusted code, leave CLR access off or combine a minimal assembly list with a positive TypeResolver.MemberFilter, purpose-built capability objects, and process isolation. Keep AllowGetType and AllowSystemReflection disabled unless they are explicitly required.

Arrays ​

CLR arrays default to ArrayConversionMode.Copy: scripts receive an independent native JavaScript array. Choose a connected, fixed-size wrapper explicitly:

csharp
var engine = new Engine(options =>
{
    options.Interop.ArrayConversion = ArrayConversionMode.LiveView;
    options.Interop.AllowWrite = true;
});

LiveView makes CLR-side changes visible and, with AllowWrite, lets script change elements. It is not a native JavaScript array and cannot be resized.

See Error handling for exceptions crossing the interop boundary and Performance for repeated projections.