Calling class method

[nabeelio]

Hi all,

I'm trying to determine if I'm doing something wrong - I'm piecing this together by looking at the tests. I can have multiple files, which all export a class called Rule. I'm importing each file as a separate module, so they don't conflict.

The JS looks something like:

export class Rule {
  meta = { ... }
  evaluate(param1, param2) {
    return 0
  }
}

And the code is:

engine.Modules.Add(name, script);
var jsRuleClass = engine.Modules.Import(name).Get("Rule");
var instance = engine.Construct(jsRuleClass);

// This works:
value = (JsObject) instance.GetProperty("meta").Value;

However, GetMethod() doesn't, it says "Cannot access internal method".

I guess the test is able to access the internal methods. Am I going about this the wrong way?

[lahma]

Here's an example how you would call the method with correct this using the public API:

[Fact]
public void ShouldAllowInvokeUserDefinedClass()
{
    _engine.Modules.Add("user", "export class UserDefined { constructor(v) { this._v = v; } hello(c) { return `hello ${this._v}${c}`; } }");
    var ctor =  _engine.Modules.Import("user").Get("UserDefined");
    var instance = _engine.Construct(ctor, "world");
    var result = instance.Get("hello").Call(instance, new JsValue[] { "!" });

    Assert.Equal("hello world!", result);
}

[nabeelio]

Thanks! I tried exactly that, and any references to this are undefined. Let me post a minimal example

[nabeelio]

Ok, so this returns an error. I'm using NUnit

[Test]
public void ShouldAllowInvokeUserDefinedClass()
{
    var _engine = new Engine(
        options => {
            options.Strict = true;
            options.LimitRecursion(20);
        }
    );

    _engine.Modules.Add(
        "user",
        """
        export class UserDefined {
            meta = {
                text: 'hello world'
            }

            hello() {
                return this.meta.text
            }
        }
        """
    );

    var ctor =  _engine.Modules.Import("user").Get("UserDefined");
    var instance = _engine.Construct(ctor);
    var result = instance.Get("hello").Call(instance);

    Assert.That(result, Is.EqualTo("hello world"));
}

The error:

Jint.Runtime.JavaScriptException: Cannot read property 'meta' of undefined
 ---> Error: Cannot read property 'meta' of undefined
   at hello () user:9:21
   at user:10:10
   --- End of inner exception stack trace ---
   at Jint.Runtime.ExceptionHelper.ThrowJavaScriptException(Engine engine, JsValue value, Completion& result)
   at Jint.Native.Function.ScriptFunction.Call(JsValue thisObject, JsValue[] arguments)
   at Jint.Engine.Call(Function function, JsValue thisObject, JsValue[] arguments, JintExpression expression)
   at Jint.Engine.<>c__DisplayClass133_0.<Call>g__Callback|0()
   at Jint.Engine.ExecuteWithConstraints[T](Boolean strict, Func`1 callback)
   at Jint.Engine.Call(JsValue callable, JsValue thisObject, JsValue[] arguments)
   at Jint.Engine.Call(JsValue callable, JsValue[] arguments)
   at Jint.JsValueExtensions.Call(JsValue value, JsValue arg1)
   at VSE.Tests.SampleRuleRunnerTest.ShouldAllowInvokeUserDefinedClass() in /Users/206675592/dev/nabeelio/acars/VSE.Tests/SampleRuleRunnerTest.cs:line 69
   at System.RuntimeMethodHandle.InvokeMethod(Object target, Void** arguments, Signature sig, Boolean isConstructor)
   at System.Reflection.MethodBaseInvoker.InvokeWithNoArgs(Object obj, BindingFlags invokeAttr)

Same thing if I add an empty constructor()

[nabeelio]

This also is the same:

export class UserDefined {
    constructor() {
        this.meta = {
            text: 'hello world'
        }
    }

    hello() {
        return this.meta.text
    }
}

[lahma]

Looks like you are passing instance as first argument instead or thisObj, see my example with first parameter as this and separate args array.

[nabeelio]

Oh, that's subtle. I see it now... thanks! That's really interesting