2722. Join Two Arrays by ID

Given two arrays arr1 and arr2 of objects, merge them into a new array based on their id property. If two objects share the same id, combine their properties with arr2's values taking precedence.

📄 Problem Statement

Each object in arr1 and arr2 contains a numeric id field.

Merge objects with the same id.
Include properties from both objects. If a key exists in both, arr2's value overrides.
If an id only appears in one array, include that object as is.
The result array should be sorted by id in ascending order.

💡 Example


arr1 = [
  {"id": 1, "x": 1},
  {"id": 2, "x": 9}
]

arr2 = [
  {"id": 2, "y": 10},
  {"id": 3, "z": 5}
]

joinArrays(arr1, arr2)
// ➞ [
//   {"id": 1, "x": 1},
//   {"id": 2, "x": 9, "y": 10},
//   {"id": 3, "z": 5}
// ]

🧠 Explanation

Use a map to store objects by their id. Loop through both arrays, and for each object:

If id already exists, merge the current object into the existing one (with arr2 overriding arr1).
Else, add it to the map.

After processing, convert the map’s values to an array and sort by id.

✅ Your Solution


/**
 * @param {Array} arr1
 * @param {Array} arr2
 * @return {Array}
 */
function joinArrays(arr1, arr2) {
    const map = new Map();

    for (const obj of arr1) {
        map.set(obj.id, { ...obj });
    }

    for (const obj of arr2) {
        if (map.has(obj.id)) {
            map.set(obj.id, { ...map.get(obj.id), ...obj });
        } else {
            map.set(obj.id, { ...obj });
        }
    }

    return Array.from(map.values()).sort((a, b) => a.id - b.id);
}