JavascriptCore hangs when running a JS with callback - objective-c

Question

I am trying to run a JS function using JavascriptCore from Objective-C. Here's the JS code:
var FeedParser = require('feedparser');
var run = function(data, options){
var feedparser = new FeedParser(options);
feedparser.on('readable', function() {
if(callback){
callback(this.read());
}
});
feedparser.end(data);
};
module.exports = {
run: run
};
And here's the Objective-C code that invokes the JS:
NSString *path = [[NSBundle mainBundle] pathForResource:#"rss" ofType:#"js"];
NSStringEncoding encoding;
NSError *error = nil;
NSString *js = [NSString stringWithContentsOfFile:path
usedEncoding:&encoding
error:&error];
JSContext *context = [[JSContext alloc] init];
[context setExceptionHandler:^(JSContext *context, JSValue *value) {
NSLog(#"%#", value);
}];
context[#"callback"] = ^(JSValue *val){
#try{
if([val isString]){
NSLog(#"%#", [val toString]);
} else if([val toDictionary][#"0"]){
NSLog(#"%#", [val toArray]);
} else {
NSLog(#"%#", [val toDictionary]);
}
}
#catch(NSException *e){
}
};
[context evaluateScript:js];
JSValue *parse = context[#"rss"][#"run"];
[parse callWithArguments:#[data, o]];
Note:
Just to be clear, this approach works fine for all other JS functions that immediately return results. I am using browserify to package them all into a single JS. I'm just noticing problems with functions that return asynchronously via callback. (Notice I'm adding callback function to the context.
When I run this on XCode it hangs (not just the app but also the XCode editor itself, and it never recovers until I kill the process from Activity Monitor).
However for some reason it returns the result as soon as I unplug the iPhone from my laptop. (At this point XCode is still in a limbo state until I kill it)
Once detached from XCode, the app runs fine. It just hangs while it's running from XCode invoked run.

Answer 1

Probably you are trying to convert some JavaScript value to NSDictionary via toDictionary call. This method attempts to convert value recursively, so it leads to a hung often. I suspect that any JS value with circular references causes infinite recursion in this case. Try to work with JSValue directly instead.