Async functions should be able to throw exceptions

[ignatandrei]

I cannot figure how the interpreter is raising errors when something got wrong ( for example , a

new Date('foo-bar')

)

[cpcallen]

The expression new Date('foo-bar') does not throw any exception; instead it returns Date object with internal value NaN:

> (new Date('foo-bar')).valueOf()
<- NaN

Otherwise, I am not sure what you are asking.

• Are you asking how to catch an exception thrown by a built-in? They may be caught in the usual way:

try {
  new Array(-1); 
} catch (e) {
  // e is RangeError: Invalid array length
}

• Are you asking how to detect if a piece of interpreted code threw an uncaught exception? This can be done by putting a try/catch around the call to .step or .run; an unhandled Error object within the interpreter will be converted into the corresponding native Error type and thrown; other values will be converted to a string and thrown as a string value.
• Are you curious about how exception handling is implemented internally in JS Interpreter? If so, there are many details but the main piece of machinery is the Interpreter.prototype.unwind method. But the implementation details should not be relevant to you unless you are proposing to modify JS Interpreter itself.

[ignatandrei]

I have tried to put a catch block around .run. It did not catch the exception. I will be back with some example to run ( on Docker ;-) )
Thanks for you answer

[cpcallen]

Let me repeat myself: the expression new Date('foo-bar') does not throw any exception.

[ignatandrei]

Now I have a good example:

please go to https://netcoreblockly.herokuapp.com/blockly.html
( it is open source and generates blockly from WebAPI definition - not important now)

There is a link in the bottom of the page named ignatandrei/NETCoreBlockly#7

It will generate some block that call an HTTP backend that throws an 500 error.
You can find the XHR function that throws an error in blockly\BlocklyXHRWrapper.js function

How can I intercept this error with the Interpreter from blockly.html ?

Thanks
Andrei

[cpcallen]

Oh, OK. You are asking about throwing exceptions, from async native functions, rather than catching them.

Async functions can throw exceptions, using the following procedure:

1. Create an Error (or subclass) object by calling myInterpreter.createObject or .createObjectProto; call this error.
2. Call myInterpreter.unwind(Interpreter.Completion.THROW, error, undefined)
3. Set myInterpreter.paused_ = false
4. And of course ensure that myInterpreter.run() will get called again, to resume execution.

Steps 1 and 4 will always be your responsibility, but steps 2 and 3 really ought to be provided by the JS Interpreter itself—for example, via #178.

[ignatandrei]

If I understand, I will write in my code:

let error= myInterpreter.createObject( { err: 'this is my error'})

Where an error to be raised , I call

myInterpreter.unwind(Interpreter.Completion.THROW, error, undefined)

This is all , right?
I will try ASAP.( and thanks for the answer)

[ignatandrei]

I tried to copy the code from here:

var error = myInterpreter.createObject(interpreter.ERROR);
myInterpreter.setProperty(error, 'message',
req.status + req.statusText,
Interpreter.NONENUMERABLE_DESCRIPTOR);
callback(undefined, error);

but it gives me:

: Non object prototype
Please help

[cpcallen]

Not sure where you're copying from, but it looks like your first line should read either

var error = myInterpreter.createObject(myInterpreter.ERROR)

or

var error = interpreter.createObject(interpreter.ERROR)

depending on the name of the variable containing your Interpreter instance.