localStorage is a client persistent storage solution provided by HTML5, suitable for saving small data such as user preferences. 1. It has a long life cycle and does not lose data after closing the page or browser; 2. The scope is homologous and supports multi-tag sharing; 3. It can only store strings, and objects need to be converted by JSON.stringify(); 4. Common APIs include setItem, getItem, removeItem and clear; 5. The storage upper limit is usually 5MB, and an error will be reported after exceeding the limit; 6. Pay attention to performance, security and cross-domain issues when using it.
Using HTML5's localStorage API for persistent data storage is actually a very practical trick. It is not like cookies that every request is transmitted to the server, but is directly stored in the browser, suitable for storing some data such as user preferences and status information. The point is that it is "persistent" and will not be lost even if the page is closed.
1. What is localStorage? What are the characteristics?
localStorage is a client storage method provided by HTML5, which is similar to sessionStorage, but the difference is:
- Different life cycles : sessionStorage closes the tab page and is gone, localStorage remains until manually cleared or deleted.
- Different scopes : they are all homologous restrictions, but do not affect cross-tab communication. Multiple tabs can read and write the same localStorage data.
It can only store strings, so if you want to store objects or arrays, you have to use JSON.stringify() to turn them first.
2. How to use it? The basic operation is very simple
The localStorage API is very simple, and several commonly used methods:
- Save data:
localStorage.setItem('key', 'value') - Get data:
localStorage.getItem('key') - Delete data:
localStorage.removeItem('key') - Clear all:
localStorage.clear()
For example, if you want to remember the user's nickname:
//Save localStorage.setItem('username', 'JohnDoe'); // Take const name = localStorage.getItem('username'); console.log(name); // Output JohnDoe // Delete localStorage.removeItem('username');
Note that if you don't delete it, this value will always exist, even if you refresh the page, close it and open the website, it will still be there.
3. How big data can be stored? Are there any restrictions?
Although it is called "persistent storage", it is not infinite space. Generally speaking:
- The browser usually allocates about 5MB of space to localStorage
- Different browsers may differ slightly, such as Chrome and Firefox are slightly different
- If the capacity is exceeded, a QUOTA_EXCEEDED_ERR error will be thrown
So don't think about using it to save large files or large amounts of structural data. If you find that you can't save it, it may be over.
4. What issues should be paid attention to when using it?
There are several details that are easy to get stuck:
- Only strings can be stored , and the object is remembered by JSON.stringify()
- Synchronous operation , frequent reading and writing may affect performance (but generally not too serious)
- Security issues : Do not store sensitive information, because it is stored in plain text
- Cross-domain isolation : localStorage under different domain names is completely independent
For example, if you want to save a user settings object:
const settings = {
theme: 'dark',
fontSize: 16,
};
// Make correct approach localStorage.setItem('userSettings', JSON.stringify(settings));
// When reading, parse must come back and const stored = localStorage.getItem('userSettings');
const parsedSettings = stored ? JSON.parse(stored) : null;Basically that's it. localStorage is quite convenient, but not omnipotent. It is very appropriate to use the right scenario, such as remembering user preferences and caching small data.
The above is the detailed content of Persistent Data Storage with HTML5 localStorage API. For more information, please follow other related articles on the PHP Chinese website!
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