Why reduce() Is Ruining Your JavaScript Code (and What to Use Instead)
5 min read
Oct 7, 2025
Why reduce() Is Ruining Your JavaScript Code (and What to Use Instead)
One thing I have encountered in JavaScript regularly is the famous grouping operation on Arrays. Whether you’re organizing products by category, sorting logs by severity level, or grouping users by subscription tier, the pattern is everywhere.
Before ES2024, we had to write less readable reduce() implementations or reach for external libraries like Lodash.
The new features in ES2024 aren’t just syntactic changes. They are performance improvements as well. It allows you to turn complex data transformations into one-liners.
Let me show you exactly why these native grouping methods are revolutionizing how we handle arrays in JavaScript.
The Problem of reduce() Overload
I used to think that JavaScript reduce() is the all rounder solution for array transformations. Need to group data? Write a reduce(). Need to count occurrences? Another reduce().
But here’s the dirty secret nobody talks about: reduce() for grouping is complex, error-prone, and a cognitive burden.
The reduce() Burden
Every time you needed to group data, you’d write something like this:
const tasks = [
{ id: 1, title: ‘Fix login bug’, priority: ‘high’, assignee: ‘Sarah’ },
{ id: 2, title: ‘Update docs’, priority: ‘low’, assignee: ‘Mike’ },
{ id: 3, title: ‘Code review’, priority: ‘high’, assignee: ‘Sarah’ },
{ id: 4, title: ‘Deploy staging’, priority: ‘medium’, assignee: ‘Alex’ }
];
// The old, painful way
const groupedByPriority = tasks.reduce((groups, task) => {
const priority = task.priority;
if (!groups[priority]) {
groups[priority] = ;
}
groups[priority].push(task);
return groups;
}, {});
This pattern repeats endlessly across codebases.
Mental Overhead
Each time you write this, you’re managing:
- An accumulator object
- Conditional initialization of array properties
- The grouping logic itself
- Return statements
That’s an overhead that distracts from your actual business logic.
The Debugging Nightmare
Here’s what happens when things go wrong with reduce():
// Oops, forgot the initial value
const broken = tasks.reduce((acc, task) => {
const status = task.status;
if (!acc[status]) {
acc[status] = ;
}
acc[status].push(task);
return acc;
}); // using undefined as key
These bugs are hidden and hard to debug, especially when you’re starting out.
Native Grouping Methods
ES2024 introduces two elegant methods that eliminate all this complexity:
Object.groupBy()- Returns a plain object with string keysMap.groupBy()- Returns a Map with any type of keys
Both methods follow the same simple pattern:
GroupingMethod(array, callbackFunction)
The callback function receives each item and returns the key to group it under. That’s it. No accumulator, no initialization, no manual key checking.
Object.groupBy() in Action
Here’s the same task grouping, but with Object.groupBy():
const tasks = [
{ id: 1, title: ‘Fix login bug’, priority: ‘high’, assignee: ‘Sarah’ },
{ id: 2, title: ‘Update docs’, priority: ‘low’, assignee: ‘Mike’ },
{ id: 3, title: ‘Code review’, priority: ‘high’, assignee: ‘Sarah’ },
{ id: 4, title: ‘Deploy staging’, priority: ‘medium’, assignee: ‘Alex’ }
];
// The modern way
const groupedByPriority = Object.groupBy(tasks, task => task.priority);
console.log(groupedByPriority);
// {
// high: [
// { id: 1, title: ‘Fix login bug’, priority: ‘high’, assignee: ‘Sarah’ },
// { id: 3, title: ‘Code review’, priority: ‘high’, assignee: ‘Sarah’ }
// ],
// low: [
// { id: 2, title: ‘Update docs’, priority: ‘low’, assignee: ‘Mike’ }
// ],
// medium: [
// { id: 4, title: ‘Deploy staging’, priority: ‘medium’, assignee: ‘Alex’ }
// ]
// }
One line. No boilerplate. No room for those sneaky bugs. Just pure, declarative intent.
Key points:
- Keys are automatically converted to strings
- Empty arrays are created automatically
- The callback receives both the item and its index
Advanced Grouping Logic
The callback function can implement complex grouping criteria:
const products = [
{ name: ‘Laptop’, price: 1200, category: ‘electronics’ },
{ name: ‘Desk Chair’, price: 300, category: ‘furniture’ },
{ name: ‘Monitor’, price: 400, category: ‘electronics’ },
{ name: ‘Coffee Mug’, price: 15, category: ‘kitchen’ }
];
// Group by price range
const groupedByPriceRange = Object.groupBy(products, product => {
if (product.price < 50) return ‘budget’;
if (product.price < 500) return ‘mid-range’;
return ‘premium’;
});
console.log(groupedByPriceRange);
// {
// budget: [{ name: ‘Coffee Mug’, price: 15, category: ‘kitchen’ }],
// ‘mid-range’: [
// { name: ‘Desk Chair’, price: 300, category: ‘furniture’ },
// { name: ‘Monitor’, price: 400, category: ‘electronics’ }
// ],
// premium: [{ name: ‘Laptop’, price: 1200, category: ‘electronics’ }]
// }
Map.groupBy() for Complex Keys
When you need non-string keys or want to maintain insertion order, Map.groupBy() is your friend.
const inventory = [
{ name: ‘apples’, type: ‘fruit’, quantity: 50 },
{ name: ‘broccoli’, type: ‘vegetable’, quantity: 5 },
{ name: ‘bananas’, type: ‘fruit’, quantity: 3 },
{ name: ‘spinach’, type: ‘vegetable’, quantity: 12 }
];
// Define objects as keys for semantic meaning
const restockNeeded = { restock: true, urgent: true };
const stockOk = { restock: false, urgent: false };
const groupedByStockStatus = Map.groupBy(inventory, item =>
item.quantity < 10 ? restockNeeded : stockOk
);
console.log(groupedByStockStatus.get(restockNeeded));
// [
// { name: ‘broccoli’, type: ‘vegetable’, quantity: 5 },
// { name: ‘bananas’, type: ‘fruit’, quantity: 3 }
// ]
The power here is using actual objects as keys, not just strings.
Key differences:
- Keys maintain their original type (no string conversion)
- Uses Map methods (
.has(),.set(),.get()) - Preserves insertion order of keys
When to Use Object.groupBy() vs Map.groupBy()
The choice between Object.groupBy() and Map.groupBy() depends on your specific needs.
Use Object.groupBy() When:
- Your keys are strings or will become strings
- You need JSON serialization. For example: you need to send the grouped data over an API or store it in
localStorage,Object.groupBy()produces JSON-serializable results. - You want simple object property access.
Use Map.groupBy() When:
- Your keys are complex objects. For example: when you need to group by numbers, objects, or other non-string values.
- Maps preserve the order in which keys were first added.
- When you want to use
.keys(),.values(),.entries(), or other Map-specific methods.
Performance Considerations
Both methods outperform custom reduce() implementations in most scenarios. Object.groupBy() has slight performance advantages for simple string-key grouping, while Map.groupBy() excels when you need the additional features that Maps provide.
Browser Support and Compatibility
Both methods are supported in modern browsers since March 2024 :
- Chrome 117+ (September 2023)
- Firefox 119+ (October 2023)
- Safari 17.4+ (March 2024)
- Edge 117+ (September 2023)
Common Pitfalls to Avoid
These are the most important things that I always keep in mind when working with these methods:
- Remember that
Object.groupBy()converts all keys to strings. - Both methods share references to the original objects.
Final Takeaway
The native groupBy() methods represent a major step forward in JavaScript’s evolution toward more expressive, readable code.
They eliminate the mental overhead of reduce()-based grouping while providing better performance and cleaner syntax.
Try it out in your next project. I would love to hear your suggestions and thoughts in comments below.
Thank you. Let’s meet again with another cool JavaScript nugget.
Written by Amit Kumar
Amit Kumar is a frontend developer who love designing web applications with clean, consistent User Interface.