javascript ios objective-c uiwebview javascriptcore

Is it possible to call an Objective-C function that returns a value to javascript?

I'd like to use JavaScriptCore / JSContext in an iOS Objective-C webview app to return a value to a javascript function.

For example, in javascript: var retVal = myObjC.returnSomething();

where returnSomething is the Objective-C function. For sake of discussion let's say it returns a string to the javascript function.

I've been able to call Objective-C functions that don't return a value, but haven't been able to find anything that describes how to return a value.

Is this even possible with JavaScriptCore, or am I taking the wrong approach to this? I need the javascript to wait for the return value (synchronous).

Solution

As you are expecting, passing data from obj C to JS use stringByEvaluatingJavaScriptFromString / passing data from JS to Obj C use JSContext

<!-- save as .html and load into UIWebview -->

    <!DOCTYPE html>
    <html>
    <head>
    <script>
    function loadData(x){
    alert(x);
    }    
    function myMeg(){   
    passDatatoObjC("success");    
    }
    </script>
    </head>
    </html>

    function returnSomething(x){
    loadData(x);
    }

    function passDatatoObjC(x){
    passDatatoObjC(x);    
    }

    #pragma mark - UIWebview dataource

    -(void)webViewDidFinishLoad:(UIWebView *)webView{

      [self.svgWebMapView   stringByEvaluatingJavaScriptFromString:@"returnSomething(10)"];

      JSContext *context =  [webView valueForKeyPath:@"documentView.webView.mainFrame.javaScriptContext"];
    context[@"passDatatoObjC"] = ^(NSString *msg) {
    NSLog(@"%@",msg);

    });
    }