LocalStorage vs IndexedDB: JavaScript Guide (Storage, Limits & Best Practices)

When building web applications, efficient data storage is essential. JavaScript provides two key client-side storage options: LocalStorage and IndexedDB. This blog will cover their differences, usage, limits, and best practices.

1. What is LocalStorage?

LocalStorage is a simple key-value storage API that allows storing small amounts of data in the browser.

Features:

• Stores data as strings.
• Synchronous (may block UI).
• Limited to ~5MB per origin.
• Persistent storage (data remains after page refresh or browser restart).
• No indexing or query support.

Use Cases:

• Caching small data (e.g., user preferences, themes).
• Storing authentication tokens (consider security risks).
• Saving basic app settings.

How to Use LocalStorage

Set Data

localStorage.setItem("username", "JohnDoe");

Get Data

const user = localStorage.getItem("username");
console.log(user); // "JohnDoe"

Remove Data

localStorage.removeItem("username");

Clear All Data

localStorage.clear();

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2. What is IndexedDB?

IndexedDB is a low-level, asynchronous, NoSQL database for storing large amounts of structured data.

Features:

• Stores objects (not just strings).
• Asynchronous (non-blocking operations).
• Much larger storage capacity (can use up to 50% of available disk space).
• Supports transactions and indexing for faster queries.
• Persistent storage (data is not cleared unless deleted by user/browser policy).

Use Cases:

• Storing large datasets (e.g., product catalogs, offline data sync).
• Storing images, files, or blobs.
• Caching API responses efficiently.

How to Use IndexedDB

Open or Create a Database

const request = indexedDB.open("MyDatabase", 1);

request.onupgradeneeded = function(event) {
  const db = event.target.result;
  if (!db.objectStoreNames.contains("users")) {
    db.createObjectStore("users", { keyPath: "id" });
  }
};

Add Data

request.onsuccess = function(event) {
  const db = event.target.result;
  const txn = db.transaction("users", "readwrite");
  const store = txn.objectStore("users");

  store.add({ id: 1, name: "Alice", age: 25 });

  txn.oncomplete = () => console.log("Data added!");
};

Read Data

request.onsuccess = function(event) {
  const db = event.target.result;
  const txn = db.transaction("users", "readonly");
  const store = txn.objectStore("users");

  const getRequest = store.get(1);
  getRequest.onsuccess = () => console.log(getRequest.result);
};

Delete Data

request.onsuccess = function(event) {
  const db = event.target.result;
  const txn = db.transaction("users", "readwrite");
  const store = txn.objectStore("users");

  store.delete(1);
  txn.oncomplete = () => console.log("Data deleted!");
};

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3. LocalStorage vs IndexedDB: Key Differences

Feature	LocalStorage	IndexedDB
Data Type	Strings	Objects (JSON, files, blobs)
Capacity	~5MB	Up to 50% of disk space
Performance	Synchronous (blocks UI)	Asynchronous (non-blocking)
Query Support	No	Yes (Indexed queries)
Transactions	No	Yes (ACID transactions)
Security	Exposed to JavaScript (XSS risk)	More secure (sandboxed)

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4. Storage Limits & Best Practices

Storage Limits

• LocalStorage: Limited to ~5MB per origin.
• IndexedDB: Can use gigabytes of space, but browsers may prompt users when reaching high storage.
• Safari Warning: Safari may auto-delete IndexedDB data if storage is low.

Best Practices

• Use LocalStorage for small, simple key-value storage.
• Use IndexedDB for complex data, large files, or offline functionality.
• Compress data (e.g., JSON.stringify + gzip for LocalStorage).
• Handle errors (e.g., QuotaExceededError in LocalStorage).
• Use navigator.storage.estimate() to check available space.

navigator.storage.estimate().then(({ quota, usage }) => {
  console.log(`Used: ${usage} bytes`);
  console.log(`Total available: ${quota} bytes`);
});

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5. Conclusion: Which One Should You Use?

Use Case	Recommended Storage
Small settings, themes	LocalStorage
User authentication tokens	LocalStorage (short-term, with security considerations)
Large datasets (e.g., e-commerce products)	IndexedDB
Offline caching	IndexedDB
Images, files, blobs	IndexedDB
Fast, indexed queries	IndexedDB

For most modern web apps, IndexedDB is the better choice due to scalability, performance, and security. However, LocalStorage is useful for quick and simple storage needs.