How to merge properties of two JavaScript objects and prefer not null values?

Question

Here are two objects:

const obj1 = {a: null, b: "b"} 
const obj2 = {a: "a", b: null}

How can I merge the two objects and get the following object?

{a: "a", b: "b"}

I can do this:

const merged = {...obj1, ...obj2}

But it returns this:

{ a: "a", b: null }

Is there a way to merge two objects while prefering not null (nor empty, undefined, etc.) values?

Answer 1

function merge(obj1, obj2) {
  answer = {}
  for(key in obj1) {
    if(answer[key] === undefined || answer[key] === null)
      answer[key] = obj1[key];
  }
  for(key in obj2) {
    if(answer[key] === undefined || answer[key] === null)
      answer[key] = obj2[key];
  }
  return answer
}