JSFiddle - React, Tailwind, and code Playground

JavaScript

var data = [
   {
      "country":"Andorra",
      "code":"AD",
      "state":[
         {
            "state_code":"AD1",
            "state_description":"aaAndorra1"
         },
         {
            "state_code":"AD2",
            "state_description":"aaAndorra2"
         }
      ]
   }
]

var result = data.reduce(function(ar, d) {
	d.state.forEach(function(s){
  	ar.push(s.state_code)
  });
  return ar;
}, [])

console.log(result);