ype dlvType = {
  obj: object;
  key: string;
  def?: string;
  p?: string;
  undef?: string;
}

export function dlv(obj, key, def = '', undef = '') {
	key = key.split ? key.split('.') : key;
	for (let p = 0; p < key.length; p++) {
		obj = obj ? obj[key[p]] : undef;
	}
	return obj === undef ? def : obj;
}

export function delve(obj, key, def = '', undef = '') {
  return dlv(obj, key, def, undef);
}

How to use it

let obj = {
    title: 'test',
    a: {
        b: {
            c: 1,
            d: undefined,
            e: null
        }
    }
};

// populate a variable
const title = delve(obj, 'title');
 
//use string dot notation for keys
delve(obj, 'a.b.c') === 1;
 
//or use an array key
delve(obj, ['a', 'b', 'c']) === 1;
 
delve(obj, 'a.b') === obj.a.b;
 
//returns undefined if the full key path does not exist and no default is specified
delve(obj, 'a.b.f') === undefined;
 
//optional third parameter for default if the full key in path is missing
delve(obj, 'a.b.f', 'foo') === 'foo';
 
//or if the key exists but the value is undefined
delve(obj, 'a.b.d', 'foo') === 'foo';
 
//Non-truthy defined values are still returned if they exist at the full keypath
delve(obj, 'a.b.e', 'foo') === null;
 
//undefined obj or key returns undefined, unless a default is supplied
delve(undefined, 'a.b.c') === undefined;
delve(undefined, 'a.b.c', 'foo') === 'foo';
delve(obj, undefined, 'foo') === 'foo';