I have an object named facility

facility = {
    facility_id: 495867,
    facility_name: "4 Pig farms Brookvale", 
    registered_business_name: "BROOKVALE FARMS COMPANY PTY LTD",
    postcode: 2100
}

why does facility['facility_name'] and facility.facility_name both give the string.
yet only facility['registered_business_name'] works
but using facility.registered_business_name gives undefined?

What is the difference between access methods that causes facility.registered_business_name to return undefined?