JavaScript Object Key Existence Check (on Any Level)

In our day to day life of coding (specially in JavaScript) sometimes we need to check whether a key of an object exists or not. It can be on any level. For example, let's imagine we have an API response where we can get the details of a blog post.

  "title": "This is a blog post",
  "author": {
    "name": "John Doe",
    "twitter": "@johndoe"
  "details": "Details blog post"

And we are showing the response on our blog details page like this:

<h4>Author: {res.author.name || 'Anonymous'}</h4>

Everything will work fine if the author key has values. For some (wired) reason if the author key has null value, then our code will break. We might get an error like:

Uncaught TypeError: Cannot read property xyz of undefined.

To avoid this kind of situation we can create a helper function to check whether a key of an object (on any level) exists or not. Here's how I implemented the function:

export const isDefined = (ref, path) => {
  let name;
  let keys = path.split('.');

  //check if the reference object exists or not
  if (!ref || typeof ref !== 'object') return false;

  while ((name = keys.shift())) {
    if (!ref.hasOwnProperty(name)) return false;
    ref = ref[name];
  return true;

That's it! Now we can use to check the existence of a key of an object like this:

import { isDefined } from '../helper/path/object-helper';

<h4>Author: {isDefined(res, 'author.name') ? res.author.name : 'Anonymous'}</h4>

Thanks for reading this tiny post. If you have any better solution, please let me know on my twitter @sh4hids.