let context:JSContext = JSContext()!

let JSCallNativeMethod: @convention(block) (String) -> Void = { params in
  print("*** param from JavaScript: \(params)")
}

context.setObject(
  unsafeBitCast(JSCallNativeMethod, to: AnyObject.self),
  forKeyedSubscript: "methodName" as NSCopying & NSObjectProtocol
)

context.evaluateScript("methodName('hi')")
// 在 Xcode 的 console 中会输出： *** context String: hi