Access file content as stream from a client js method

  Hi, I have a json file in Vault that is linked to a property of an Item. How can I access json file stream from client side JS onload-event method ? I have tried with fetchFileProperty, which prompts user for download of the json file, but what I need is to access its file stream in js method. Any ideas, please do share. Thank you so much myItem.fetchFileProperty("jsonFile", "", 0)