Javascript hashmap equivalent

javascript

hashmap

performance

best-practices

byNikita Barsukov·Oct 9, 2024

Leverage the Map object, JavaScript's hashmap equivalent, efficiently pairing keys with values and preserving unique key types and order.

let map = new Map([['key1', 'value1'], ['key2', 'value2']]);
// "Knock knock. Who's there? 'value1'"
console.log(map.get('key1'));

Methods .set(), .get(), .has(), and .delete() offer efficient key-value manipulation which cuts out the "map-ness" from the everyday programming "madness."

Object VS Map: The face-off!

In JavaScript, Objects and Maps share similar features but also have distinctive perks.

Objects:

Key stringification: Keys convert to strings; potential overwriting risk due to key string duplication.
No size property: Size retrieval isn't provided upfront; manual iteration required.
From chaos to order: Except for integer keys, the rest hold an arbitrary ordering.

Maps:

Key type preservation: Allows for any value, including objects, as a key without stringification.
Size matters: Use the size property to quickly get the number of entries.
Insertion order hero: Ensures predictability with ordering by insertion.

Performance perks with Maps

Perform heavy lifting involving frequent insertions and removals of key-value pairs efficiently using Map - the workout buddy for your keys. Also, avoid hashing collisions by ensuring all keys maintain their uniqueness and type.

For very serious accounting of key-value pairs where Map seems to fall short, consider data libraries like Immutable.js and collections.js introducing bonus features.

Real-world scenarios featuring Maps

Maps are like Swiss Army knives, versatile for practical applications:

Memoization

In computation-intensive tasks, Maps efficiently cache results based on parameters. A faster and more efficient way to say, "Been there, done that!"

Associating data with DOM elements

Maps' ability to handle object references as keys makes it perfect to attach metadata to DOM elements without meddling with the actual elements. A sidekick you didn't know your DOM needed!

Tracking unique items

Thanks to Maps, unique items tracked efficiently. Who needs to hire a Private Investigator when you have Maps?

Complex keys

Working with multi-dimensional keys is truly a breeze with Maps. Flex your key muscles without heavy stringification thank to Maps' sportsmanship in using an array or object as a key.

Choose your weapon

Whether it's a JavaScript Object or Map, it boils down to the right tool for the job.

Object, when:

You're dealing with JSON that naturally forms a string-to-any mapping.
You're dealing with static or known key sets.

Map, if:

Keys are dynamic, complex, or non-stringable.
Insertion-order is crucial.
Large key-value pairs sets or insertion/deletion performance is a concern.

Collision detection and common pitfalls

Although Maps handle key uniqueness better than Objects, design your data structure with these in mind:

Use keys with defined equality. Enforce a clear definition.
Stay clear of non-primitive keys unless strictly necessary.
Watch out for potential leaks as objects or functions used as keys might evade garbage collection.

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