const arr = {
a: 4,
b: 6,
c: { x: 9, y: 8 }
}

const x = keyObjectFinder(this.arr, 'c.x');
console.log('result is ' + x);

helper.js
export function keyObjectFinder(obj, value) {
    if (typeof obj === 'object' && obj.constructor === Object) {
        for (const key in obj) {
            if (obj.hasOwnProperty(key)) {
                let x = obj[value];
                return x;
            }
        }
    }
}