How do I handle duplicate keys when merging two objects in JavaScript?

How do I handle duplicate keys when merging two objects in JavaScript?

When merging two objects, if they have duplicate keys, the values from the second object will overwrite those from the first. You can use the spread operator or Object.assign to merge them.

Can you show me an example using the spread operator?

Sure! Here's an example:

const obj1 = { a: 1, b: 2 };
const obj2 = { b: 3, c: 4 };
const merged = { ...obj1, ...obj2 }; // { a: 1, b: 3, c: 4 }

In this case, the value of 'b' from obj2 overwrites the value from obj1.

What if I want to keep both values for duplicate keys?

You can create a custom merge function that combines values into an array. For example:

const mergeObjects = (obj1, obj2) => {
  const result = { ...obj1 };
  for (const key in obj2) {
    if (result[key]) {
      result[key] = [result[key], obj2[key]];
    } else {
      result[key] = obj2[key];
    }
  }
  return result;
};