Flatten javascript objects into a single-depth object

Object Flatten

var flattenObject = function(ob) {
	var toReturn = {};
	
	for (var i in ob) {
		if (!ob.hasOwnProperty(i)) continue;
		
		if ((typeof ob[i]) == 'object') {
			var flatObject = flattenObject(ob[i]);
			for (var x in flatObject) {
				if (!flatObject.hasOwnProperty(x)) continue;
				
				toReturn[i + '.' + x] = flatObject[x];
			}
		} else {
			toReturn[i] = ob[i];
		}
	}
	return toReturn;
};

This is my implementation, it just flattens every object in the parent object into one, without keying them with object.key.
Working example
Code:

function flatten(obj = {}) {
  const doneObject = {}
  for (const [k, v] of Object.entries(obj)) {
    if (typeof v == "object" && !(v instanceof  Date) && !Array.isArray(v) && !(v instanceof regExp)) {
       Object.assign(doneObject, flatten(v))
    } else {
      doneObject[k] = v
    }
  }
  return doneObject
}

Thank you for the original implementation!

A version that leaves undefined behind, array as is and don't try to flatten primitive objects (Number, Boolean, BigInt and String essentially) :

const flatten = <T extends Record<string, any>>(object: T, path?: string): Record<string, any> =>
  Object.entries(object).reduce((acc, [key, val]) => {
    if (val === undefined) return acc;
    if (path) key = `${path}.${key}`;
    if (typeof val === 'object' && val !== null && !(val instanceof Date) && !(val instanceof RegExp) && !Array.isArray(val)) {
      if (val !== val.valueOf()) {
        return { ...acc, [key]: val.valueOf() };
      }
      return { ...acc, ...flatten(val, key) };
    }
    return { ...acc, [key]: val };
  }, {});