"callFunction" only allows a function to be called if it is a property of an object. "callAsFunction" allows functions to be called directly, which is more flexible.

One good application would be using callback to handle the no-return-value problem.

-(void)getValueWithCallback:(GAScriptObject*)callback{
    [callback callAsFunctionWithArguments:@[@"Hello"]];
}

GAJavaScript.performSelector( 'getValueWithCallback:', function(value){
    // value == "Hello"
});