A JavaScript function which assures that a value of a child chain property is returned without runtime errors.

JavaScriptGetNestedValues.js

const obj = {
  c: {
    a: 2,
    b: {
      c: [1, 2, 3, {a: 15, b: 10}, 15]
    },
    c: undefined,
    d: null
  }, 
  d: ''
}


/**
 * Assures that a value of a child chain property is returned without runtime errors.
 *
 * If the checked property does not exist in the provided object or one of the children in the chain
 * is undefined, then it returns the provided fallback value.
 *
 * The fallback can be also returned if the checked property is falsy (i.e. undefined, null, false, 0, '', etc.)
 * and the fallbackOnFalsy flag is set to <TRUE>.
 *
 * Arrays could be checked as well by passing the index in the path; ex: getValue(arr, '0.obj')
 *
 * Note: if object or path params are not provided, the fallback is returned.
 *
 * @param {Object|Array} object - ordinary JSON object or array in which the property value is checked.
 * @param {String | Array} path - object property access chain; ex: 'a.b.c' or ['a', 'b.c', 'd'].
 * @param {*} fallback - the fallback value.
 * @param {Boolean} fallbackOnFalsy - if true and the found property value is falsy then it returns the fallback.
 *
 * @returns {*} - the deepest property value or the fallback.
 */
getValue(object, path, fallback, fallbackOnFalsy) {
  if (!object || !path) {
      return fallback;
  }

  if (typeof path === 'string') {
     path = path.split('.');
  }

  // Reduces object properties to the deepest property in the path argument.
  return path.reduce((object, property) => {
   if (object && typeof object !== 'string' && object.hasOwnProperty(property)) {
      // The property is found but it may be falsy.
      // If fallback is active for falsy values, the fallback is returned, otherwise the property value.
      return !object[property] && fallbackOnFalsy ? fallback : object[property];
    } else {
      // Returns the fallback if current chain link does not exist or it does not contain the property.
      return fallback;
    }
  }, object);
}

// Same as get value but slightly unreadable.
// function getValue(o, path, fb, fbFalsy) {
//   if(!o || !path) return fb;
//   return path.split('.').reduce((o, p) => o && typeof o !== 'string' && o.hasOwnProperty(p) ? !o[p] && fbFalsy ? fb : o[p] : fb, o);
// }

// Shorter version. which does not apply fallback for falsy values, it just returnes what it finds.
// function getValue(o, path, fb) {
//   if(!o || !path) return fb;
//   return path.split('.').reduce((o, p) => o && typeof o !== 'string' && o.hasOwnProperty(p) ? o[p] : fb, o);
// }




// fallback
console.log(getValue(null, 'c.d.d', 'fallback'))

// fallback
console.log(getValue(obj, null, 'fallback'))

// fallback
console.log(getValue(null, null, 'fallback'))

// fallback
console.log(getValue(obj, 'c.d.d', 'fallback'))

// null
console.log(getValue(obj, 'c.d', 'fallback'));

// array
console.log(getValue(obj, 'c.b.c', 'fallback'));

// array index 2
console.log(getValue(obj, 'c.b.c.2', 'fallback'));

// no index => fallback
console.log(getValue(obj, 'c.b.c.10', 'fallback'));

// array no index, no fallback => undefined
console.log(getValue(obj, 'c.b.c.10'));

// array's object property
console.log(getValue(obj, 'c.b.c.3.a'));

// array property length
console.log(getValue(obj, 'c.b.c.length', 'fallback'));

// prints falsy object
console.log(getValue(obj, 'c.c', 'fallback'));

// prints fallback for falsy values
console.log(getValue(obj, 'c.c', 'fallback', true));

// prints fallback
console.log(getValue(obj, 'c.z.1', 'fallback'));

// prints fallback
console.log(getValue(obj, 'c.z.1', 'fallback', true));