Does anyone can explain why this code works in javascript ?

let people = [
  "Jeremy",
  "Male",
  (address = [(domicile = [{ province: "jakarta", city: "jakpus" }])]),
  (origin = [{ provinceOrigin: "Lampung", cityOrigin: "Bandar Lampung" }]),
];
console.log(address); //[ [ { province: 'jakarta', city: 'jakpus' } ] ]

does this code declare a variable inside array's element ? but why i cannot declare the variable using let, const, or var ?