How can I merge two maps in JavaScript?

How can I merge two maps in JavaScript?

You can use the Map constructor along with the spread operator to merge two maps. Here's an example:

const map1 = new Map([['a', 1], ['b', 2]]);
const map2 = new Map([['b', 3], ['c', 4]]);
const mergedMap = new Map([...map1, ...map2]);
console.log(mergedMap);

This will result in a map that contains the entries from both maps, with the second map's values overwriting the first where keys overlap.

What if I want to combine the values instead of overwriting?

In that case, you can iterate over the entries of the second map and combine the values. Here's how you can do it:

const combinedMap = new Map(map1);
map2.forEach((value, key) => {
    if (combinedMap.has(key)) {
        combinedMap.set(key, combinedMap.get(key) + value);
    } else {
        combinedMap.set(key, value);
    }
});
console.log(combinedMap);

This will sum the values for keys that exist in both maps.

Can I use the Object.assign method instead?

Object.assign is typically used for objects, not maps. However, you can convert maps to objects, merge them, and then convert back to a map. Here's an example:

const obj1 = Object.fromEntries(map1);
const obj2 = Object.fromEntries(map2);
const mergedObj = Object.assign({}, obj1, obj2);
const finalMap = new Map(Object.entries(mergedObj));
console.log(finalMap);

This approach works but is less efficient than using the spread operator.

What are some common use cases for merging maps?

Common use cases include combining configuration settings, aggregating data from multiple sources, or merging user preferences.