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Table of Contents
How to store data using localStorage?
Typical application scenarios of sessionStorage
What should you pay attention to when using Web Storage?
Home Web Front-end HTML Tutorial What is Web Storage API in HTML5 (localStorage and sessionStorage)?

What is Web Storage API in HTML5 (localStorage and sessionStorage)?

Jul 07, 2025 am 02:22 AM

The Web Storage API provides two ways for clients to store data: localStorage and sessionStorage. localStorage is used to store data permanently, and will not be lost even if the browser is closed. It is suitable for saving user preferences, topic settings and other information; sessionStorage is only valid during the current session and is cleared after closing the page or tag. It is suitable for temporary data such as form storage. Both support the setItem(), getItem(), removeItem() and clear() methods to manipulate data, but the stored data must be in string format, and the object or array must be converted through JSON.stringify(). When using it, you need to pay attention to security, capacity limitations (usually 5MB), synchronization operations may affect performance and inability to access across domains.

What is Web Storage API in HTML5 (localStorage and sessionStorage)?

The Web Storage API is a client data storage mechanism introduced by HTML5 to save key-value pair data in the browser. Compared with traditional cookies, it provides a simpler and larger storage method. There are mainly two types: localStorage and sessionStorage .

What is Web Storage API in HTML5 (localStorage and sessionStorage)?

The difference is that the data life cycle and scope of action are different:

What is Web Storage API in HTML5 (localStorage and sessionStorage)?
  • localStorage : The data is permanently saved and will not be lost even if the browser is closed unless it is actively cleared (such as calling removeItem() or clear() ).
  • sessionStorage : The data is only valid during the current session and will be cleared after closing the page or browser tag.

How to store data using localStorage?

localStorage is suitable for saving user preferences, theme settings, login status, etc. that do not require frequent changes.

Common methods include:

What is Web Storage API in HTML5 (localStorage and sessionStorage)?
  • setItem(key, value) : save data
  • getItem(key) : get data
  • removeItem(key) : delete a certain data
  • clear() : Clear all data

For example:

 // Store data localStorage.setItem('username', 'john_doe');

// Get data const user = localStorage.getItem('username');
console.log(user); // Output: john_doe

// Delete the data localStorage.removeItem('username');

It should be noted that the data in localStorage is in string format. If you want to store objects or arrays, you need to first convert them with JSON.stringify() .


Typical application scenarios of sessionStorage

sessionStorage is more suitable for temporary data storage, such as temporary storage in the middle of the form filling, cross-page parameter transmission, etc.

For example, in a multi-step registration process, user input can be temporarily saved to sessionStorage at each step so that the user does not lose the filled content when jumping to the page.

 // Save the data in the first step sessionStorage.setItem('email', 'user@example.com');

// Read const email = sessionStorage.getItem('email');

Similar to localStorage , it supports the same method names and operations, but only works in the current session.


What should you pay attention to when using Web Storage?

Although Web Storage is convenient, there are some limitations and considerations:

  • Security issues : Do not store sensitive information, such as passwords, tokens, etc., because these data can be accessed by homologous scripts.
  • Capacity limit : Most browsers support approximately 5MB of storage space, and the specific values ??may vary from browser to browser.
  • Synchronization operation : Web Storage is synchronized, and frequent reading and writing may affect performance.
  • Cannot access across domains : Only storage content under the same origin (the protocol domain name port is consistent).

If you need more complex structured data management, or want to implement asynchronous storage, you can consider using IndexedDB.


Basically that's it. The Web Storage API is simple and easy to use, but in actual development, you still need to choose the appropriate storage method according to the scenario.

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