Jint is a Javascript interpreter for .NET which can run on any modern .NET platform as it supports .NET Standard 2.0 and .NET 4.6.2 targets (and later).
Use cases and users
Run JavaScript inside your .NET application in a safe sand-boxed environment
Expose native .NET objects and functions to your JavaScript code (get database query results as JSON, call .NET methods, etc.)
Support scripting in your .NET application, allowing users to customize your application using JavaScript (like Unity games)
Some users of Jint include
RavenDB,
,
,
,
,
,
and many more.
✔ ArrayBuffer enhancements - ArrayBuffer.prototype.resize and ArrayBuffer.prototype.transfer
❌ Atomics.waitAsync
✔ Ensuring that strings are well-formed - String.prototype.ensureWellFormed and String.prototype.isWellFormed
✔ Grouping synchronous iterables - Object.groupBy and Map.groupBy
✔ Promise.withResolvers
❌ Regular expression flag /v
ECMAScript Stage 3 (no version yet)
✔ Float16Array (Jint v4, requires NET 6 target or higher)
✔ Import attributes
✔ JSON modules
✔ Promise.try (Jint v4)
✔ Set methods (intersection, union, difference, symmetricDifference, isSubsetOf, isSupersetOf, isDisjointFrom)
✔ ShadowRealm
✔ Uint8Array to/from base64
Other
Further refined .NET CLR interop capabilities
Constraints for execution (recursion, memory usage, duration)
Performance
Because Jint neither generates any .NET bytecode nor uses the DLR it runs relatively small scripts really fast
If you repeatedly run the same script, you should cache the Script or Module instance produced by Esprima and feed it to Jint instead of the content string
You should prefer running engine in strict mode, it improves performance
You can check out the engine comparison results, bear in mind that every use case is different and benchmarks might not reflect your real-world usage.
Discussion
Join the chat on Gitter or post your questions with the jint tag on stackoverflow.
Video
Here is a short video of how Jint works and some sample usage
Engine instances are not thread-safe and they should not accessed from multiple threads simultaneously.
Examples
This example defines a new value named log pointing to Console.WriteLine, then runs
a script calling log('Hello World!').
var engine = new Engine()
.SetValue("log", new Action<object>(Console.WriteLine));
engine.Execute(@"
function hello() {
log('Hello World');
};
hello();
");
Here, the variable x is set to 3 and x * x is evaluated in JavaScript. The result is returned to .NET directly, in this case as a double value 9.
var square = new Engine()
.SetValue("x", 3) // define a new variable
.Evaluate("x * x") // evaluate a statement
.ToObject(); // converts the value to .NET
You can also directly pass POCOs or anonymous objects and use them from JavaScript. In this example for instance a new Person instance is manipulated from JavaScript.
var p = new Person {
Name = "Mickey Mouse"
};
var engine = new Engine()
.SetValue("p", p)
.Execute("p.Name = 'Minnie'");
Assert.AreEqual("Minnie", p.Name);
You can invoke JavaScript function reference
var result = new Engine()
.Execute("function add(a, b) { return a + b; }")
.Invoke("add",1, 2); // -> 3
or directly by name
var engine = new Engine()
.Execute("function add(a, b) { return a + b; }");
engine.Invoke("add", 1, 2); // -> 3
Accessing .NET assemblies and classes
You can allow an engine to access any .NET class by configuring the engine instance like this:
var engine = new Engine(cfg => cfg.AllowClr());
Then you have access to the System namespace as a global value. Here is how it's used in the context on the command line utility:
jint> var file = new System.IO.StreamWriter('log.txt');
jint> file.WriteLine('Hello World !');
jint> file.Dispose();
And even create shortcuts to common .NET methods
jint> var log = System.Console.WriteLine;
jint> log('Hello World !');
=> "Hello World !"
When allowing the CLR, you can optionally pass custom assemblies to load types from.
var engine = new Engine(cfg => cfg
.AllowClr(typeof(Bar).Assembly)
);
and then to assign local namespaces the same way System does it for you, use importNamespace
jint> var Foo = importNamespace('Foo');
jint> var bar = new Foo.Bar();
jint> log(bar.ToString());
adding a specific CLR type reference can be done like this
Generic types are also supported. Here is how to declare, instantiate and use a List<string>:
jint> var ListOfString = System.Collections.Generic.List(System.String);
jint> var list = new ListOfString();
jint> list.Add('foo');
jint> list.Add(1); // automatically converted to String
jint> list.Count; // 2
Internationalization
You can enforce what Time Zone or Culture the engine should use when locale JavaScript methods are used if you don't want to use the computer's default values.
This example forces the Time Zone to Pacific Standard Time.
var PST = TimeZoneInfo.FindSystemTimeZoneById("Pacific Standard Time");
var engine = new Engine(cfg => cfg.LocalTimeZone(PST));
engine.Execute("new Date().toString()"); // Wed Dec 31 1969 16:00:00 GMT-08:00
This example is using French as the default culture.
var FR = CultureInfo.GetCultureInfo("fr-FR");
var engine = new Engine(cfg => cfg.Culture(FR));
engine.Execute("new Number(1.23).toString()"); // 1.23
engine.Execute("new Number(1.23).toLocaleString()"); // 1,23
Execution Constraints
Execution constraints are used during script execution to ensure that requirements around resource consumption are met, for example:
Scripts should not use more than X memory.
Scripts should only run for a maximum amount of time.
You can configure them via the options:
var engine = new Engine(options => {
// Limit memory allocations to 4 MB
options.LimitMemory(4_000_000);
// Set a timeout to 4 seconds.
options.TimeoutInterval(TimeSpan.FromSeconds(4));
// Set limit of 1000 executed statements.
options.MaxStatements(1000);
// Use a cancellation token.
options.CancellationToken(cancellationToken);
}
You can also write a custom constraint by deriving from the Constraint base class:
public abstract class Constraint
{
/// Called before script is run and useful when you use an engine object for multiple executions.
public abstract void Reset();
// Called before each statement to check if your requirements are met; if not - throws an exception.
public abstract void Check();
}
For example we can write a constraint that stops scripts when the CPU usage gets too high:
class MyCPUConstraint : Constraint
{
public override void Reset()
{
}
public override void Check()
{
var cpuUsage = GetCPUUsage();
if (cpuUsage > 0.8) // 80%
{
throw new OperationCancelledException();
}
}
}
var engine = new Engine(options =>
{
options.Constraint(new MyCPUConstraint());
});
When you reuse the engine and want to use cancellation tokens you have to reset the token before each call of Execute:
var engine = new Engine(options =>
{
options.CancellationToken(new CancellationToken(true));
});
var constraint = engine.Constraints.Find<CancellationConstraint>();
for (var i = 0; i < 10; i++)
{
using (var tcs = new CancellationTokenSource(TimeSpan.FromSeconds(10)))
{
constraint.Reset(tcs.Token);
engine.SetValue("a", 1);
engine.Execute("a++");
}
}
Using Modules
You can use modules to import and export variables from multiple script files:
var engine = new Engine(options =>
{
options.EnableModules(@"C:\Scripts");
})
var ns = engine.Modules.Import("./my-module.js");
var value = ns.Get("value").AsString();
By default, the module resolution algorithm will be restricted to the base path specified in EnableModules, and there is no package support. However you can provide your own packages in two ways.
Defining modules using JavaScript source code:
engine.Modules.Add("user", "export const name = 'John';");
var ns = engine.Modules.Import("user");
var name = ns.Get("name").AsString();
Defining modules using the module builder, which allows you to export CLR classes and values from .NET:
// Create the module 'lib' with the class MyClass and the variable version
engine.Modules.Add("lib", builder => builder
.ExportType<MyClass>()
.ExportValue("version", 15)
);
// Create a user-defined module and do something with 'lib'
engine.Modules.Add("custom", @"
import { MyClass, version } from 'lib';
const x = new MyClass();
export const result as x.doSomething();
");
// Import the user-defined module; this will execute the import chain
var ns = engine.Modules.Import("custom");
// The result contains "live" bindings to the module
var id = ns.Get("result").AsInteger();
Note that you don't need to EnableModules if you only use modules created using Engine.Modules.Add.
.NET Interoperability
Manipulate CLR objects from JavaScript, including:
Single values
Objects
Properties
Methods
Delegates
Anonymous objects
Convert JavaScript values to CLR objects
Primitive values
Object -> expando objects (IDictionary<string, object> and dynamic)
Array -> object[]
Date -> DateTime
number -> double
string -> string
boolean -> bool
Regex -> RegExp
Function -> Delegate
Extensions methods
Security
The following features provide you with a secure, sand-boxed environment to run user scripts.
Define memory limits, to prevent allocations from depleting the memory.
Enable/disable usage of BCL to prevent scripts from invoking .NET code.
Limit number of statements to prevent infinite loops.
Limit depth of calls to prevent deep recursion calls.
Define a timeout, to prevent scripts from taking too long to finish.
Branches and releases
The recommended branch is main, any PR should target this branch
