What does sessionStorage do?

JavaScriptJunior~2 min read

Definition

sessionStorage is a browser object that stores "key-value" pairs (strings) only while the current tab (or window) is open. Once the tab is closed, the data is automatically removed.

Put simply: it is temporary storage, available only within a single tab and domain.

1. A simple example

javascript

// Save data
sessionStorage.setItem('user', 'Tim');

// Read data
console.log(sessionStorage.getItem('user')); // "Tim"

// Remove one item
sessionStorage.removeItem('user');

// Clear the whole storage
sessionStorage.clear();

2. Difference from localStorage

Storage	Lifetime	Shared between tabs	Cleared on close
localStorage	Permanent (until cleared manually)	Yes (between tabs of the same domain)	No
sessionStorage	While the tab is open	No (each tab has its own)	Yes

In other words, if a user opens your site in a new tab, they get a new, empty sessionStorage.

3. All the methods are the same as localStorage

Method	What it does	Example
`setItem(key, value)`	Saves a value	`sessionStorage.setItem('token', 'abc')`
`getItem(key)`	Returns a value	`sessionStorage.getItem('token')`
`removeItem(key)`	Removes an item	`sessionStorage.removeItem('token')`
`clear()`	Clears everything	`sessionStorage.clear()`
`key(index)`	Returns the key at an index	`sessionStorage.key(0)`
`length`	Number of entries	`sessionStorage.length`

4. Example: form data kept while the tab is open

javascript

<input id="name" placeholder="Name" />

<script>
  const input = document.getElementById('name');

  // Restore the value on page reload
  input.value = sessionStorage.getItem('name') || '';

  // Save on change
  input.addEventListener('input', () => {
    sessionStorage.setItem('name', input.value);
  });
</script>

Now the entered name survives a page reload, but if you close the tab and open the site again, the field clears.

5. Example: storing data for a single authorization session only

javascript

sessionStorage.setItem('sessionToken', 'abc123');

// the token survives a page reload
console.log(sessionStorage.getItem('sessionToken')); // "abc123"

// but disappears when the tab is closed

This is used when you need to store:

a token or login state only until the window closes,
temporary data (for example, form or filter state),
data "drafts" that do not need to persist.

6. Important details

Works only with strings, so for objects:

javascript
sessionStorage.setItem('user', JSON.stringify({ name: 'Tim' })); const user = JSON.parse(sessionStorage.getItem('user'));
Storage capacity is roughly 5 MB.
Data is accessible only from the same domain and tab.
You can use the storage event, but it does not fire in the same window, only between tabs (which is usually irrelevant for sessionStorage).

Summary

Parameter	`localStorage`	`sessionStorage`
Storage lifetime	Forever (until cleared)	While the tab is open
Access between tabs	Yes	No
Cleared when the window closes	No	Yes
Capacity	~5-10 MB	~5 MB
Data type	Strings only	Strings only
Common use	Settings, themes, user data	Temporary sessions, forms, filters

Remember it simply:

localStorage is "forever",

sessionStorage is "while the tab is open".

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