// Say what the thing is
interface MyThingy {
  name: string,
  age: number,
  address: string,
  [key: string]: string|number
}
// Include that when declaring the variable
var datasource: MyThingy[] = [
  { name: 'x', age: 20, address: 'yyyy' },
  { name: 's', age: 30, address: 'zzzz' }
];

let keys: Object[] = Object.keys(datasource[0]);
let dlen: number = datasource.length as number;
while (dlen--) {
    let kLn: number = keys.length;
    while (kLn--) {
        let key: string = keys[kLn] as string;
        let mkey: string | number; // Since age is number, the other two are strings
        if (key == "age") {
            mkey = datasource[dlen][key] as number;
        } else {
            mkey = datasource[dlen][key] as string;
        }

    }
}