JavaScript: Deep check objects have same keys

Question

Question is similar to: How can I check that two objects have the same set of property names? but only one difference

I want to check:

var objOne = {"a":"one","b":"two","c":{"f":"three_one"}};
var objTwo = {"a":"four","b":"five","c":{"f":"six_one"}};

have the same set of keys in all level?

For example deepCheckObjKeys(objOne, objTwo) would return true where deepCheckObjKeys(objOne, objThree) return false, if:

var objThree = {"a":"four","b":"five","c":{"g":"six_one"}};

Since objThree.a.c.f is undefined in objThree.

A function like this:

'use strict';

function objectsHaveSameKeys() {
   for (var _len = arguments.length, objects = Array(_len), _key = 0; _key < _len; _key++) {
      objects[_key] = arguments[_key];
   }

   var allKeys = objects.reduce(function (keys, object) {
      return keys.concat(Object.keys(object));
   }, []);
   var union = new Set(allKeys);
   return objects.every(function (object) {
      return union.size === Object.keys(object).length;
   });
}

only checks the first level.

PS: objectsHaveSameKeys() ES6 equivalent:

function objectsHaveSameKeys(...objects):boolean {
   const allKeys = objects.reduce((keys, object) => keys.concat(Object.keys(object)), []);
   const union = new Set(allKeys);
   return objects.every(object => union.size === Object.keys(object).length);
}

Answer 1

I'd do a recursive check if a property's value is an object.

There's an interesting wrinkle here; actually, there are (at least) two:

• What if one of the "objects" is null and the other has no properties? true or false?
• What if one of the objects has {a: null} and the other has {a: 17}? true or false?
• What if one of the objects has {a: null} and the other has {a: {}}? true or false?

For the purposes of this example, I've treated null like an object with no properties, but it's very much dependent on your use case. I can think of at least two other ways to go (null doesn't match anything but null, or null doesn't match anything but a non-object, even if the object has no own properties) and there are probably others.

See comments:

const deepSameKeys = (o1, o2) => {
    // Both nulls = same
    if (o1 === null && o2 === null) {
        return true;
    }

    // Get the keys of each object
    const o1keys = o1 === null ? new Set() : new Set(Object.keys(o1));
    const o2keys = o2 === null ? new Set() : new Set(Object.keys(o2));
    if (o1keys.size !== o2keys.size) {
        // Different number of own properties = not the same
        return false;
    }

    // Look for differences, recursing as necessary
    for (const key of o1keys) {
        if (!o2keys.has(key)) {
            // Different keys
            return false;
        }
        
        // Get the values and their types
        const v1 = o1[key];
        const v2 = o2[key];
        const t1 = typeof v1;
        const t2 = typeof v2;
        if (t1 === "object") {
            if (t2 === "object" && !deepSameKeys(v1, v2)) {
                return false;
            }
        } else if (t2 === "object") {
            // We know `v1` isn't an object
            return false;
        }
    }

    // No differences found
    return true;
};

// Checking your example
const objOne   = {"a": "one",  "b": "two",  "c": {"f": "three_one"}};
const objTwo   = {"a": "four", "b": "five", "c": {"f": "six_one"}};
const objThree = {"a": "four", "b": "five", "c": {"g": "six_one"}};

console.log("objOne vs. objTwo:         ", deepSameKeys(objOne, objTwo));        // true
console.log("objTwo vs. objThree:       ", deepSameKeys(objTwo, objThree));      // false

// `null` checks
console.log("{a: null} vs. {a: 17}      ", deepSameKeys({a: null}, {a: 17}));    // true
console.log("{a: null} vs. {a: {}}      ", deepSameKeys({a: null}, {a: {}}));    // true -- depending on your use case, you may want this to be false
console.log("{a: null} vs. {a: {x:1}}   ", deepSameKeys({a: null}, {a: {x:1}})); // false

// Differing value type check
console.log("{a: 1} vs. {a: '1'}}       ", deepSameKeys({a: 1}, {a: '1'}));      // true

Answer 2

I guess you're looking for a deep-check version of the function provided [here] :)(How can I check that two objects have the same set of property names?).

Below is my attempt. Please note:

• Solution does not check for null and is not bullet proof
• I haven't performance tested it. Maybe the OP or anyone else can do that and share for the community.
• I'm not a JS expert :).

function objectsHaveSameKeys(...objects) {
  const allKeys = objects.reduce((keys, object) => keys.concat(Object.keys(object)), [])
  const union = new Set(allKeys)
  if (union.size === 0) return true
  if (!objects.every((object) => union.size === Object.keys(object).length)) return false

  for (let key of union.keys()) {
    let res = objects.map((o) => (typeof o[key] === 'object' ? o[key] : {}))
    if (!objectsHaveSameKeys(...res)) return false
  }
  return true
}