


What is the Web Storage API, and how do I use it to store data in the browser?
Jun 25, 2025 pm 01:45 PMThe Web Storage API provides two storage methods: localStorage and sessionStorage. localStorage is used to store data for a long time, and it will not be lost even if the browser is closed; sessionStorage is only valid when the current tab or window is open. Both store key-value pairs in the form of strings, and complex types need to be converted with JSON.stringify(). Common operations include setItem(), getItem(), removeItem() and clear(). Suitable for storing small, non-sensitive information such as user preferences and form data, and is not suitable for storing sensitive or large-scale data. When using it, you should pay attention to the correct processing of the data type and choose the appropriate storage method.
The Web Storage API is a simple way to store data in a user's browser. Unlike cookies, which get sent back to the server with every request, Web Storage keeps data locally — meaning it's faster and more efficient for client-side use. There are two main storage options: localStorage
and sessionStorage
. The key difference? localStorage
persists even after the browser is closed, while sessionStorage
only lasts as long as the current tab or window is open.
What Can You Store with Web Storage?
Web Storage works like a key-value store, where both keys and values ??are strings. That means you can't directly store complex types like objects or arrays without first converting them into strings (usually via JSON.stringify()
).
For example:
localStorage.setItem('username', 'johndoe'); sessionStorage.setItem('cartItems', JSON.stringify(['item1', 'item2']));
If you try to store something else — like a number or an object — it won't throw an error, but it will be converted to a string automatically, which might not give you what you expect.
Common things people store include:
- User preferences (like theme settings)
- Form input values ??(to restore after refresh)
- Temporary state information (eg, login status)
How to Use localStorage and sessionStorage
Using either localStorage
or sessionStorage
follows the same basic pattern. Here's how to do the most common operations:
Set a value
localStorage.setItem('theme', 'dark');
Get a value
const currentTheme = localStorage.getItem('theme');
Remove a value
localStorage.removeItem('theme');
Clear all stored values
localStorage.clear();
These methods work exactly the same with sessionStorage
, just with a shorter lifespan.
A few things to note:
- If a key doesn't exist,
getItem()
returnsnull
. - Keys are scoped per origin (domain protocol), so one site can't access another's storage.
- Storage limits are much larger than cookies — usually around 5MB.
Handling Data Types Correctly
Since Web Storage only accepts strings, storing non-string values ??require conversion:
To save an array or object:
const user = { name: 'Alice', age: 30 }; localStorage.setItem('user', JSON.stringify(user));
To retrieve and parse it back:
const userData = JSON.parse(localStorage.getItem('user')); console.log(userData.name); // Alice
This pattern is very common, but it's easy to forget the JSON.stringify()
or JSON.parse()
, especially when debugging. A good practice is to wrap these operations in helper functions if you're using them often.
Also, remember that:
- Functions won't survive
JSON.stringify()
- Dates will become strings and need re-conversion
- Deeply nested objects may cause performance issues if too large
When to Use localStorage vs sessionStorage
Choosing between the two comes down to how long you want the data to last .
Use localStorage
when:
- You want to remember user choices across sessions (eg, dark mode preference)
- You're caching data that should persist even after the browser closes
Use sessionStorage
when:
- You're storing temporary info that shouldn't stick around (eg, form drafts)
- You need to keep data isolated between tabs (each tab has its own
sessionStorage
)
One thing to watch out for: sessionStorage
is tied to the tab, not the browser window. So if someone opens a new tab to the same site, that tab starts fresh.
Storing data in the browser with the Web Storage API is straightforward and useful for many small-scale needs. It's not mean for sensitive or large-scale data, but for simple client-side storage, it gets the job done. Just remember to handle data types correctly and choose the right storage type based on your use case.
Basically that's it.
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