How to write a file into IOS device in ionic 3

I have a JSON file i just need to write that file into my external folder

I am able to write the file in Android but i am getting a problem in IOS can anyone help me with this??

what error is showing iOS?

@AxelStone thanks for the reply
Actually i am able to write file in ios also but i dont know where exactly the file is storing in ios device.
and i am using this as my path this.file.documentsDirectory