Crash when passing Swift objects to JavaScript

Question

I'm trying to use a Swift class with JavaScriptCore. This is what I have:

import JavaScriptCore

@objc(MyObjExport) // explicit name required for class_copyProtocolList to work
public protocol MyObjExport: JSExport {
    var foo: String! { get }
}

@objc(MyObj)
public class MyObj: NSObject, MyObjExport
{
    public var foo: String! { return "bar" }
}

Which produces the following "MyModule-Swift.h" header:

SWIFT_PROTOCOL("MyObjExport")
@protocol MyObjExport <JSExport>
@property (nonatomic, readonly, copy) NSString * foo;
@end

SWIFT_CLASS("MyObj")
@interface MyObj : NSObject <MyObjExport>
@property (nonatomic, readonly, copy) NSString * foo;
@end

I can create and use this object just fine from other Obj-C code, but:

MyObj *foo = [[MyObj alloc] init];

[JSValue valueWithObject:foo inContext:nil]; // EXC_BAD_ACCESS

It crashes in the JSCore implementation:

#0  0x00007fff87c5ca73 in objectToValueWithoutCopy(JSContext*, objc_object*) ()
#1  0x00007fff87c5c27e in objectToValue(JSContext*, objc_object*) ()
#2  0x00007fff87c5c20c in +[JSValue valueWithObject:inContext:] ()

(Nothing is logged to the console.) If I implement the class in Obj-C instead of Swift, it works fine. What's wrong and how can I fix this?

dbotha · Accepted Answer · 2014-11-17 22:56:54Z

1

Surely you don't want the JSContext that you're passing creating the JSValue with to be nil?

I tried with a non-nil context and I can successfully instantiate a JSValue, with a nil context it crashes with EXC_BAD_ACCESS.

This would work:

JSContext *context = [[JSContext alloc] init];
MyObj *foo = [[MyObj alloc] init];
[JSValue valueWithObject:foo inContext:context];

answered Nov 17, 2014 at 22:56

dbotha

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