Custom field in jalik:ufs

When i upload a file to the store this is what it looks like in the db:

{ 
    "_id" : "TNQHaTRk9DrCo4ARt", 
    "store" : "photos", 
    "name" : "bloc2-kristal-ap.-37.jpg", 
    "lastModified" : 1438611678000, 
    "lastModifiedDate" : ISODate("2015-08-03T14:21:18Z"), 
    "webkitRelativePath" : "", 
    "size" : 137791, "type" : "image/jpeg", 
    "complete" : true, 
    "uploading" : false, 
    "extension" : "jpg", 
    "progress" : 1, 
    "userId" : "yT4at8Tpuu39WjakL", 
    "token" : "AbEB5Bab28", 
    "uploadedAt" : ISODate("2016-08-23T08:20:31.343Z"), 
    "url" : "http://localhost:3000/ufs/photos/TNQHaTRk9DrCo4ARt/bloc2-kristal-ap.-37.jpg" 
}

When i create this ,how can i add a custom field like “formID”: “xxx” ?