Tool-jint

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Jint

sebastienros/jint: Javascript Interpreter for .NET (github.com)

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 up).

💡 You should prefer 3.x beta over the 2.x legacy version as all new features and improvements are targeted against version 3.x.

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 add = new Engine()
    .Execute("function add(a, b) { return a + b; }")
    .GetValue("add");

add.Invoke(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

engine.SetValue("TheType", TypeReference.CreateTypeReference(engine, typeof(TheType)))

and used this way

jint> var o = new TheType();

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 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.FindConstraint<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.ImportModule("./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.CreateModule("user", "export const name = 'John';")

var ns = engine.ImportModule("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.CreateModule("lib", builder => builder
    .ExportType<MyClass>()
    .ExportValue("version", 15)
);

// Create a user-defined module and do something with 'lib'
engine.CreateModule("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.ImportModule("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 AddModule.

.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