Records vs Maps in JavaScript

Introduction

In JavaScript, there are many methods you can use to represent key-value pairs, which is a fundamental task. Among these data structures, Records and Maps are two powerful options that serve different purposes and offer unique advantages. In this article, we will explore the differences between Records and Maps, their practical applications, and the type of data structures they represent.

1. What Are Records in JavaScript?

In JavaScript, Records are analogous to Objects. A Record is essentially an object where the keys are strings (or symbols), and the values can be of any data type.

Example:

const user = #{
    firstName: 'John',
    lastName: 'Doe',
    age: 30,
    email: 'john.doe@example.com'
};

Here, the user object is a Record, with firstName, lastName, age, and email as keys.

Characteristics of Records:

Key Types: Keys are typically strings or symbols.
Order: JavaScript objects DO NOT guarantee the order of keys, although in practice, they are often iterated in the order they were created.
Performance: Fast lookups (O(1)) due to direct hash-based indexing of keys.
Static Nature: Best suited for scenarios where keys are known and relatively static.

2. Understanding Maps in JavaScript

Maps in JavaScript are built-in objects that allow storing key-value pairs where both the keys and values can be of any data type. This flexibility makes Maps more versatile than Records (plain objects).

Example:

const map = new Map();
map.set('name', 'Alice');
map.set(42, 'The Answer');
map.set(true, 'Boolean Key');

In this example, the map object uses a string, a number, and a boolean as keys, demonstrating the flexibility of Map.

Characteristics of Maps:

Key Types: Keys can be of any type (objects, functions, primitives).
Order: Map preserves the order of insertion, meaning entries are iterated in the order they were added.
Performance: Optimized for dynamic operations like frequent additions and deletions.
Dynamic Nature: Suitable for scenarios where keys may change or need to be of various types.

3. Key Differences Between Records and Maps

Understanding the distinctions between Records (objects) and Maps is important for selecting the right data structure for your application. You can consider what type of key types you will be needing, if you need to preserve the order of the entries, and the common operations you will be completing on the data structure in order to increase performance. Both Records and Maps have their own trade-offs in these regards.

Key Types

Records: Keys must be strings or symbols.
Maps: Keys can be of any type, including objects, arrays, and functions.

Order of Entries

Records: Key order is not guaranteed but usually reflects the order of insertion (with some exceptions for numeric keys).
Maps: Keys maintain the order of insertion, making iteration predictable.

Performance Considerations

Records: Generally faster for static key lookups because they are directly hashed.
Maps: May be slightly slower for lookups due to the added complexity of handling any key type, but they are optimized for dynamic use cases.

4. Practical Examples

Using Records for Static Data

Consider a scenario where you need to store user profile information, which is relatively static and well-defined. A Record can work well here:

const userProfile = #{
    name: 'Jane Smith',
    age: 28,
    email: 'jane.smith@example.com',
    isAdmin: false
};

Here, a Record (plain object) is ideal because the structure of the data is predictable and does not require complex key types.

Leveraging Maps for Dynamic Data

Suppose you need to manage a cache where keys might be objects or functions, and you need to add or remove entries dynamically. A Map can work well here:

const cache = new Map();
const key1 = { id: 1 };
const key2 = function() { return 'key'; };

cache.set(key1, 'Object as key');
cache.set(key2, 'Function as key');

// Iterating over the map
cache.forEach((value, key) => {
    console.log(key, value);
});

A Map is the appropriate choice here due to its flexibility with key types and dynamic nature.

5. Choosing the Right Data Structure

In general, you can follow these rules when deciding between using either of the data structures:

Use Records (objects) when:
- You need a simple structure with string/symbol keys.
- The keys are relatively static and known ahead of time.
- You prioritize fast lookups and minimal overhead.
Use Maps when:
- You need flexible key types (beyond just strings).
- The data structure requires frequent additions, deletions, or dynamic key management.
- Order of insertion is important.

6. Thanks for Reading!

Records and Maps in JavaScript offer distinct advantages for handling key-value pairs. Understanding their differences, from key types to performance characteristics, is essential for making the right choice in your projects. Use Records for static, simple data structures and Maps for dynamic, complex scenarios where key flexibility and insertion order are crucial.

I hope you enjoyed this quick article! Thanks for reading!

Jeremy Quinto