Swift JSContext onload触发器

我需要将那一堆代码从Objective-c重写为swift：

    JSContext *jsContext = [webView valueForKeyPath:@"documentView.webView.mainFrame.javaScriptContext"];
jsContext[@"loaded"] = ^{
    NSLog(@"Content Loaded!");
};

---

问题在于加载webView时获取上下文。

找到了swift的解决方案：

 if let jsContext = svtwebView?.value(forKeyPath: "documentView.webView.mainFrame.javaScriptContext") as? JSContext {
                let loaded: @convention(block) () -> Void = {
                    print("Loaded:")
                }
                jsContext.setObject(loaded, forKeyedSubscript: "loaded" as NSCopying & NSObjectProtocol)
                jsContext.evaluateScript("loaded")
            }