HTML LocalStorage and SessionStorage

LocalStorage and SessionStorage are Web Storage API features that let web applications store data in the browser as key–value pairs for client-side state management.

• Store data as key–value pairs in the browser.
• LocalStorage persists data even after the browser is closed.
• SessionStorage stores data for a single browser session.
• Data is accessible only within the same origin.
• Useful for client-side preferences, tokens, and temporary state.

SessionStorage

SessionStorage stores data on the client side for the duration of a single browser tab or session.

• Used for temporary client-side data storage.
• Storage limit is approximately 5 MB.
• Data persists only while the current tab is open.
• Data is automatically cleared when the tab is closed.

Note: When a closed tab is restored (Ctrl + Shift + T), SessionStorage may persist in Chrome and Firefox but not in Safari. This behavior is browser-dependent.

LocalStorage

LocalStorage is used to store data on the client side with no expiration time, allowing data to persist until it is manually removed.

• Stores data on the client side.
• Storage limit is approximately 5 MB.
• Data persists even after the browser is closed.
• Data is removed only when the user clears it.
• Main difference from SessionStorage is data persistence.

Below are the details about SessionStorage and LocalStorage:

1. Both are Object type

Both SessionStorage and LocalStorage are object-based storage mechanisms that store data as key–value pairs in the browser.

2. Format of storing data in SessionStorage and LocalStorage:

Data must be stored in key-value pair in the SessionStorage and LocalStorage and key-value must be either number or string

• Data stored in LocalStorage as a string or number is saved and retrieved correctly.
• When a plain JavaScript object is stored directly, it is automatically converted to a string.
• As a result, retrieving the object returns "[object Object]" instead of the actual data.
• This occurs because LocalStorage only supports string value.

LocalStorage.setItem("geek", {
"key":"value"
})
undefined
LocalStorage.getItem("geek")
"[object Object]"

To store objects or non-string data in LocalStorage, they must first be converted into a string.

LocalStorage.setItem("geeks", JSON.stringify({
"key":"value"
}))
undefined
LocalStorage.getItem("geeks")
"{"key":"value"}"

In this attempt we use JSON.stringify() method to convert an object into string.

Common Methods

Listed below are the commonly used methods of LocalStorage and SessionStorage.

1. For storing data in web storage

Use setItem() to store key–value pairs (values are stored as strings).

LocalStorage.setItem("key", "value");  //key and value both should be string or number;
SessionStorage.setItem("key", "value");  //key and value both should be string or number;

2. For getting data from web storage

Use getItem(key) to retrieve the value associated with the given key from storage.

LocalStorage.getItem("key");
SessionStorage.getItem("key");

Here we will pass the key and it will return value.

3. For Getting the length of web storage object

Use the length property to get the total number of stored key–value pairs.

LocalStorage.length; 
SessionStorage.length;

4. For deleting a particular key-value pair

Use removeItem(key) to delete the stored data associated with the specified key from Web Storage.

LocalStorage.removeItem("key");
SessionStorage.removeItem("key");

5. For clearing complete storage

Use the clear() method to remove all key–value pairs from LocalStorage or SessionStorage.

LocalStorage.clear();
SessionStorage.clear();

6. For getting nth key name from web storage we will pass the number n

Use the key(n) method to retrieve the name of the key at index n from storage.

LocalStorage.key(n);
SessionStorage.key(n);

Note:

• Web Storage stores data in plain text, so sensitive information like passwords or payment details should never be stored there.
• Web Storage is accessible only on the client side; for server-side data storage, cookies are a better option.

Storing Non-String values with JSON

Web Storage supports only string values, so objects and arrays must be converted to strings before storing.

• Use JSON.stringify() to convert an object or array into a string.
• Store the string in localStorage or sessionStorage.
• Use JSON.parse() to convert the stored string back into its original form.

let gfgObj = { name: "GeeksForGeeks", score: "100" };
localStorage.setItem(key, JSON.stringify(gfgObj));

let item = JSON.parse(localStorage.getItem(key));

Note: The same approach works for sessionStorage as well.