Check if a JavaScript object has a given value or key

When working with plain JavaScript objects, you'll often need to check if a value or key exists. While the JavaScript API for objects isn't as rich as that for arrays, it still provides a few methods that can help you with this task.

Check if an object has a given value

In order to check if an object has a given value, you can use Object.values() to get all the values of the object. Then, use Array.prototype.includes() to check if the target value is included in the values array.

const hasValue = (obj, value) => Object.values(obj).includes(value);

const obj = { a: 100, b: 200 };
hasValue(obj, 100); // true
hasValue(obj, 999); // false

Check if an object has a given key

Checking if an object has a given key is equally as easy, using Object.keys() instead of Object.values(). Then, you can use Array.prototype.includes() to check if the target key is included in the keys array.

const hasKey = (obj, key) => Object.keys(obj).includes(key);

const obj = { a: 100, b: 200 };
hasKey(obj, 'a'); // true
hasKey(obj, 'c'); // false

Accounting for nested keys

Checking for nested keys is a bit more complex, but can be done with a little ingenuity.

Given an array of keys, you can use Array.prototype.every() to sequentially check the keys to the internal depth of the object. Using Object.prototype.hasOwnProperty(), you can then check if the object does not have the current key or is not an object, stop propagation and return false. Otherwise, assign the key's value to the object to use on the next iteration.

const hasKeyDeep = (obj, keys) => {
  return (
    keys.length > 0 &&
    keys.every(key => {
      if (typeof obj !== 'object' || !obj.hasOwnProperty(key)) return false;
      obj = obj[key];
      return true;
    })
  );
};

let obj = {
  a: 1,
  b: { c: 4 },
  'b.d': 5
};
hasKeyDeep(obj, ['a']); // true
hasKeyDeep(obj, ['b']); // true
hasKeyDeep(obj, ['b', 'c']); // true
hasKeyDeep(obj, ['b.d']); // true
hasKeyDeep(obj, ['d']); // false
hasKeyDeep(obj, ['c']); // false
hasKeyDeep(obj, ['b', 'f']); // false