Lodash Merge not updating object with correct values - arrays

Question

I am trying to merge these two objects using Lodash merge.
Server object:
[
{
"id": "74738",
"customerId": "534430"
},
{
"id": "74742",
"customerId": "534429"
}
]
Local Object
[
{
"customerId": "534429"
"name": "ABC"
},
{
"customerId": "534430",
"name": "XYZ"
},
]
I am using lodash merge to combine these two objects based on attributes, I am using this code below:
merge({}, serverObject, localObject);
// Output: [{"id":"74738","customerId":"534429","name":"ABC"},{"id":"74742","customerId":"534430","name":"XYZ"}]
The object is not being updated based on the Customer Ids but instead by the sequence of local object.
Expected Output:
[{"id":"74738","customerId":"534430","name":"ABC"},{"id":"74742","customerId":"534429","name":"XYZ"}]

Answer 1

With lodash you can combine all arrays to a single one using _.flatten(), group by a predicate, and then map and merge each group to a single object.
Note: since your customerId is an integer, the items would be ordered by the numerical value.
const { map, groupBy, flatten, merge } = _
const fn = (predicate, ...arrs) => map(
groupBy(flatten(arrs), predicate),
group => merge({}, ...group)
)
const arr1 = [{"id":"74738","customerId":"534430"},{"id":"74742","customerId":"534429"}]
const arr2 = [{"customerId":"534429","name":"ABC"},{"customerId":"534430","name":"XYZ"}]
const result = fn('customerId', arr1, arr2)
console.log(result)
<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.21/lodash.min.js" integrity="sha512-WFN04846sdKMIP5LKNphMaWzU7YpMyCU245etK3g/2ARYbPK9Ub18eG+ljU96qKRCWh+quCY7yefSmlkQw1ANQ==" crossorigin="anonymous" referrerpolicy="no-referrer"></script>
If you need to preserve the original order, flatten to a single array, and then reduce the items to a Map using the result of the predicate as the key. Merge each new item with the same key to the existing one in the Map. Convert the Map's values back to an array using Array.from():
const fn = (predicate, ...arrs) => Array.from(arrs
.flat()
.reduce((acc, o) => {
const key = predicate(o)
return acc.set(key, { ...acc.get(key), ...o })
}, new Map()).values()
)
const arr1 = [{"id":"74738","customerId":"534430"},{"id":"74742","customerId":"534429"}]
const arr2 = [{"customerId":"534429","name":"ABC"},{"customerId":"534430","name":"XYZ"}]
const result = fn(o => o.customerId, arr1, arr2)
console.log(result)