Handling duplicate keys in a JavaScript Map while using reduce() with an array of objects
I'm migrating some code and I've spent hours debugging this and I'm trying to merge an array of objects into a Map in JavaScript using the `reduce` method... The question arises when there are duplicate keys in the objects because my current implementation overwrites the existing keys instead of merging their values. Here's what I have: ```javascript const data = [ { id: 1, value: 'A' }, { id: 2, value: 'B' }, { id: 1, value: 'C' } ]; const mergedMap = data.reduce((map, obj) => { map.set(obj.id, obj.value); // This causes overwriting of value return map; }, new Map()); console.log(mergedMap); ``` This results in the Map showing only the last value for each key: ``` Map(2) { 1 => 'C', 2 => 'B' } ``` I want `mergedMap` to retain all values for duplicate keys, perhaps in an array format, like this: ``` Map(2) { 1 => ['A', 'C'], 2 => ['B'] } ``` I tried changing the value assignment to push into an array, but I run into issues when the key doesn't exist yet: ```javascript const mergedMap = data.reduce((map, obj) => { if (!map.has(obj.id)) { map.set(obj.id, []); } map.get(obj.id).push(obj.value); return map; }, new Map()); ``` However, I received a TypeError when trying to push to an undefined value. Can anyone guide to troubleshoot this scenario? What am I missing here? I'm using Javascript 3.11 in this project. I'm working in a CentOS environment. Thanks, I really appreciate it! This is for a desktop app running on Debian. How would you solve this? I'm on Debian using the latest version of Javascript. Any help would be greatly appreciated! My team is using Javascript for this application. Could someone point me to the right documentation?