Safety merge objects

safeMergeObjects.js

export default function safeMerge(obj1, obj2) {
  const keys = Object.keys(obj2).concat(Object.keys(obj1));
  const isInvalid = val => val === undefined || Number.isNaN(val) || val === null;
  return keys.reduce((acc, key) => {
    acc[key] = !isInvalid(obj2[key])
      ? obj2[key]
      : obj1[key];

    if (isInvalid(acc[key])) {
      delete acc[key];
    }

    return acc;
  }, {});
}

/**
 * Examples:
 */

safeMerge(
  { foo: 'bar', fizz: 'buzz' },
  { magic: 'xyzzy', fizz: undefined, foo: null }
)
// { foo: 'bar', fizz: 'buzz', magic: 'xyzzy' }  

safeMerge(
  { magic: 'xyzzy', foo: null },
  { fizz: 'buzz' }
)
// { magic: 'xyzzy', fizz: 'buzz' }