JINT - Unable to "console.log"

Question

I am new to JINT, and trying to just do some basic tests to kind of learn the ropes. My first attempt was to just store some javascript in my database, load it, and execute it in a unit test. So that looks essentially like this....

[Fact]
public void can_use_jint_engine() {
    using (var database = DocumentStore()) {
        using (var session = database.OpenSession()) {
            var source = session.Load<Statistic>("statistics/1");

            // join the list of strings into a single script
            var script = String.Join("\n", source.Scripting);

            // this will create the script
            // console.log("this is a test from jint.");
            // 
            var engine = new Jint.Engine();
            // attempt to execute the script
            engine.Execute(script);
        }
    }
}

And it doesn't work, I get this error, which makes absolutely no sense to me, and I cannot find any documentation on.

Jint.Runtime.JavaScriptExceptionconsole is not defined at Jint.Engine.Execute(Program program) at Jint.Engine.Execute(String source) at SampleProject.Installers.Instanced.__testing_installer.can_use_jint_engine() in _testing_installer.cs: line 318

Can anyone assist in shedding some light on this? I'm pretty confused at this point.

Answer 1

With JavaScript there are three entities - we care about. The host (browser, your application etc), the engine (JINT in this case) and the script ("console.log(...)") in this case.

JavaScript defines a bunch of functions and object as part of the language, but console is not one of them. By convention, browsers define a console object that can be used in the manner you describe. However, since your app is not a browser (and JINT does not do this by itself), there's no console object defined in your namespace (globals).

What you need to do is add a console object that will be accessible in JINT. You can find how to do this in the docs, but here's a simple example of how to add a log function to the engine so it can be used from the JS code (example taken from github).

var engine = new Engine()
        .SetValue("log", new Action<object>(Console.WriteLine))
        ;

    engine.Execute(@"
      function hello() { 
        log('Hello World');
      };

      hello();
    ");