Calling [JSValue callWithArguments:] locks UI when alert() is called

Question

Using the JSContext from a UIWebView I have created a javascript function that is implemented as an Objective C block:

JSContext *js =          


        

Answer 1

After a couple days looking at stack traces of threads waiting for each other, the solution was so simple I'm not surprised I overlooked it in favor of trying more complicated stuff.

If you want to call back into a UIWebView's javascript asynchronously, use window.setTimeout and let the JSVirtualMachine take care of queuing the callback.

Just replace

dispatch_async(dispatch_get_main_queue(), ^{
    [self.callback callWithArguments:@[arg]];
});

with

dispatch_async(dispatch_get_main_queue(), ^{
    [self.callback.context[@"setTimeout"] callWithArguments:@[self.callback, @0, arg]];
});