Persistent storage can help protect critical data from eviction, and reduce the
chance of data loss.
 Pete LePage [X](https://twitter.com/petele) [GitHub](https://github.com/petele) [Mastodon](https://techhub.social/@petele) [Homepage](https://petelepage.com/)
When faced with storage pressure like low disk space, browsers will
typically [evict data](https://web.dev/storage-for-the-web#eviction), including from the Cache API and IndexedDB,
from the least recently used origin. This may cause data loss if the app
hasn't synced data with the server, and reduce the reliability of the app by
removing resources required for the app to work, both of which lead to
negative user experiences.
Thankfully, research by the Chrome team shows that data is very rarely
cleared automatically by Chrome. It is far more common for users to manually
clear storage. Thus if a user visits your site regularly, the chances are
small that your data will be evicted. To prevent the browser from deleting
your data, you can request that your entire site's storage be marked
persistent.
> [!NOTE]
> **Note:** Only request that critical site data is marked as persistent (for example, end-to-end encryption keys), data that if not backed up to the cloud, could result in significant data loss. Persistent storage is kept by the browser, even if storage is running low. It's only deleted if the user chooses to remove it using their site settings.
Persistent storage is [supported in many modern](https://caniuse.com/#feat=mdn-api_permissions_persistent-storage_permission) browsers.
Browser Support
- ' d='M96 183a64 64 0 0 1-23-23L17 64a128 128 0 0 0 111 192l55-96a64 64 0 0 1-87 23Z'/%3E%3Cpath fill='url(%23b)' d='M192 128a64 64 0 0 1-9 32l-55 96A128 128 0 0 0 239 64H128a64 64 0 0 1 64 64Z'/%3E%3Ccircle cx='128' cy='128' r='52' fill='%231a73e8'/%3E%3Cpath fill='url(%23c)' d='M96 73a64 64 0 0 1 32-9h111a128 128 0 0 0-222 0l56 96a64 64 0 0 1 23-87Z'/%3E%3C/svg%3E)
- ' xlink:href='%23A'%3E%3Cstop offset='.76' stop-opacity='0'/%3E%3Cstop offset='.95' stop-opacity='.5'/%3E%3Cstop offset='1'/%3E%3C/radialGradient%3E%3CradialGradient id='F' cx='2523' cy='4680' r='20243' gradientTransform='matrix(-.03715 .99931 -2.12836 -.07913 13579 3530)' xlink:href='%23A'%3E%3Cstop offset='0' stop-color='%2335c1f1'/%3E%3Cstop offset='.11' stop-color='%2334c1ed'/%3E%3Cstop offset='.23' stop-color='%232fc2df'/%3E%3Cstop offset='.31' stop-color='%232bc3d2'/%3E%3Cstop offset='.67' stop-color='%2336c752'/%3E%3C/radialGradient%3E%3CradialGradient id='G' cx='24247' cy='7758' r='9734' gradientTransform='matrix(.28109 .95968 -.78353 .22949 24510 -16292)' xlink:href='%23A'%3E%3Cstop offset='0' stop-color='%2366eb6e'/%3E%3Cstop offset='1' stop-color='%2366eb6e' stop-opacity='0'/%3E%3C/radialGradient%3E%3Cpath id='H' d='M24105 20053a9345 9345 0 01-1053 472 10202 10202 0 01-3590 646c-4732 0-8855-3255-8855-7432 0-1175 680-2193 1643-2729-4280 180-5380 4640-5380 7253 0 7387 6810 8137 8276 8137 791 0 1984-230 2704-456l130-44a12834 12834 0 006660-5282c220-350-168-757-535-565z'/%3E%3Cpath id='I' d='M11571 25141a7913 7913 0 01-2273-2137 8145 8145 0 01-1514-4740 8093 8093 0 013093-6395 8082 8082 0 011373-859c312-148 846-414 1554-404a3236 3236 0 012569 1297 3184 3184 0 01636 1866c0-21 2446-7960-8005-7960-4390 0-8004 4166-8004 7820 0 2319 538 4170 1212 5604a12833 12833 0 007684 6757 12795 12795 0 003908 610c1414 0 2774-233 4045-656a7575 7575 0 01-6278-803z'/%3E%3Cpath id='J' d='M16231 15886c-80 105-330 250-330 566 0 260 170 512 472 723 1438 1003 4149 868 4156 868a5954 5954 0 003027-839 6147 6147 0 001133-850 6180 6180 0 001910-4437c26-2242-796-3732-1133-4392-2120-4141-6694-6525-11668-6525-7011 0-12703 5635-12798 12620 47-3654 3679-6605 7996-6605 350 0 2346 34 4200 1007 1634 858 2490 1894 3086 2921 618 1067 728 2415 728 2952s-271 1333-780 1990z'/%3E%3Cuse fill='url(%23B)' xlink:href='%23H'/%3E%3Cuse fill='url(%23D)' opacity='.35' xlink:href='%23H'/%3E%3Cuse fill='url(%23C)' xlink:href='%23I'/%3E%3Cuse fill='url(%23E)' opacity='.4' xlink:href='%23I'/%3E%3Cuse fill='url(%23F)' xlink:href='%23J'/%3E%3Cuse fill='url(%23G)' xlink:href='%23J'/%3E%3C/svg%3E)
- ' gradientUnits='userSpaceOnUse'%3E%3Cstop offset='.2' stop-color='%239059ff' stop-opacity='0'/%3E%3Cstop offset='.3' stop-color='%238c4ff3' stop-opacity='.1'/%3E%3Cstop offset='.8' stop-color='%237716a8' stop-opacity='.5'/%3E%3Cstop offset='1' stop-color='%236e008b' stop-opacity='.6'/%3E%3C/radialGradient%3E%3CradialGradient id='ff-g' cx='239.1' cy='34.6' r='171.6' gradientUnits='userSpaceOnUse'%3E%3Cstop offset='0' stop-color='%23ffe226'/%3E%3Cstop offset='.1' stop-color='%23ffdb27'/%3E%3Cstop offset='.3' stop-color='%23ffc82a'/%3E%3Cstop offset='.5' stop-color='%23ffa930'/%3E%3Cstop offset='.7' stop-color='%23ff7e37'/%3E%3Cstop offset='.8' stop-color='%23ff7139'/%3E%3C/radialGradient%3E%3CradialGradient id='ff-h' cx='374' cy='-74.3' r='732.2' gradientUnits='userSpaceOnUse'%3E%3Cstop offset='.1' stop-color='%23fff44f'/%3E%3Cstop offset='.5' stop-color='%23ff980e'/%3E%3Cstop offset='.6' stop-color='%23ff5634'/%3E%3Cstop offset='.7' stop-color='%23ff3647'/%3E%3Cstop offset='.9' stop-color='%23e31587'/%3E%3C/radialGradient%3E%3CradialGradient id='ff-i' cx='304.6' cy='7.1' r='536.4' gradientTransform='rotate(84 303 4)' gradientUnits='userSpaceOnUse'%3E%3Cstop offset='0' stop-color='%23fff44f'/%3E%3Cstop offset='.1' stop-color='%23ffe847'/%3E%3Cstop offset='.2' stop-color='%23ffc830'/%3E%3Cstop offset='.3' stop-color='%23ff980e'/%3E%3Cstop offset='.4' stop-color='%23ff8b16'/%3E%3Cstop offset='.5' stop-color='%23ff672a'/%3E%3Cstop offset='.6' stop-color='%23ff3647'/%3E%3Cstop offset='.7' stop-color='%23e31587'/%3E%3C/radialGradient%3E%3CradialGradient id='ff-j' cx='235' cy='98.1' r='457.1' gradientUnits='userSpaceOnUse'%3E%3Cstop offset='.1' stop-color='%23fff44f'/%3E%3Cstop offset='.5' stop-color='%23ff980e'/%3E%3Cstop offset='.6' stop-color='%23ff5634'/%3E%3Cstop offset='.7' stop-color='%23ff3647'/%3E%3Cstop offset='.9' stop-color='%23e31587'/%3E%3C/radialGradient%3E%3CradialGradient id='ff-k' cx='355.7' cy='124.9' r='500.3' gradientUnits='userSpaceOnUse'%3E%3Cstop offset='.1' stop-color='%23fff44f'/%3E%3Cstop offset='.2' stop-color='%23ffe141'/%3E%3Cstop offset='.5' stop-color='%23ffaf1e'/%3E%3Cstop offset='.6' stop-color='%23ff980e'/%3E%3C/radialGradient%3E%3ClinearGradient id='ff-a' x1='446.9' y1='76.8' x2='47.9' y2='461.8' gradientUnits='userSpaceOnUse'%3E%3Cstop offset='.1' stop-color='%23fff44f'/%3E%3Cstop offset='.1' stop-color='%23ffe847'/%3E%3Cstop offset='.2' stop-color='%23ffc830'/%3E%3Cstop offset='.4' stop-color='%23ff980e'/%3E%3Cstop offset='.4' stop-color='%23ff8b16'/%3E%3Cstop offset='.5' stop-color='%23ff672a'/%3E%3Cstop offset='.5' stop-color='%23ff3647'/%3E%3Cstop offset='.7' stop-color='%23e31587'/%3E%3C/linearGradient%3E%3ClinearGradient id='ff-l' x1='442.1' y1='74.8' x2='102.6' y2='414.3' gradientUnits='userSpaceOnUse'%3E%3Cstop offset='.2' stop-color='%23fff44f' stop-opacity='.8'/%3E%3Cstop offset='.3' stop-color='%23fff44f' stop-opacity='.6'/%3E%3Cstop offset='.5' stop-color='%23fff44f' stop-opacity='.2'/%3E%3Cstop offset='.6' stop-color='%23fff44f' stop-opacity='0'/%3E%3C/linearGradient%3E%3C/defs%3E%3Cpath d='M479 166c-11-25-32-52-49-60a249 249 0 0 1 25 73c-27-68-73-95-111-155a255 255 0 0 1-8-14 44 44 0 0 1-4-9 1 1 0 0 0 0-1 1 1 0 0 0-1 0c-60 35-81 101-83 134a120 120 0 0 0-66 25 71 71 0 0 0-6-5 111 111 0 0 1-1-58c-25 11-44 29-58 44-9-12-9-52-8-60l-8 4a175 175 0 0 0-24 21 210 210 0 0 0-22 26 203 203 0 0 0-32 73l-1 2-2 15a229 229 0 0 0-4 34v1a240 240 0 0 0 477 40l1-9c5-41 0-84-15-121zM202 355l3 1-3-1zm55-145zm198-31z' fill='url(%23ff-a)'/%3E%3Cpath d='M479 166c-11-25-32-52-49-60 14 26 22 53 25 72v1a207 207 0 0 1-206 279c-113-3-212-87-231-197-3-17 0-26 2-40-2 11-3 14-4 34v1a240 240 0 0 0 477 40l1-9c5-41 0-84-15-121z' fill='url(%23ff-b)'/%3E%3Cpath d='M479 166c-11-25-32-52-49-60 14 26 22 53 25 72v1a207 207 0 0 1-206 279c-113-3-212-87-231-197-3-17 0-26 2-40-2 11-3 14-4 34v1a240 240 0 0 0 477 40l1-9c5-41 0-84-15-121z' fill='url(%23ff-c)'/%3E%3Cpath d='m362 195 1 1a130 130 0 0 0-22-29C266 92 322 5 331 0c-60 35-81 101-83 134l9-1c45 0 84 25 105 62z' fill='url(%23ff-d)'/%3E%3Cpath d='M257 210c-1 6-22 26-29 26-68 0-80 41-80 41 3 35 28 64 57 79l4 2 7 3a107 107 0 0 0 31 6c120 6 143-143 57-186 22-4 45 5 58 14-21-37-60-62-105-62l-9 1a120 120 0 0 0-66 25l17 16c16 16 58 33 58 35z' fill='url(%23ff-e)'/%3E%3Cpath d='M257 210c-1 6-22 26-29 26-68 0-80 41-80 41 3 35 28 64 57 79l4 2 7 3a107 107 0 0 0 31 6c120 6 143-143 57-186 22-4 45 5 58 14-21-37-60-62-105-62l-9 1a120 120 0 0 0-66 25l17 16c16 16 58 33 58 35z' fill='url(%23ff-f)'/%3E%3Cpath d='m171 151 5 3a111 111 0 0 1-1-58c-25 11-44 29-58 44 1 0 36 0 54 11z' fill='url(%23ff-g)'/%3E%3Cpath d='M18 261a242 242 0 0 0 231 197 207 207 0 0 0 206-279c8 56-20 110-64 146-86 71-169 43-186 31l-3-1c-50-24-71-70-67-110-42 0-57-35-57-35s38-28 89-4c46 22 90 4 90 4 0-2-42-19-58-35l-17-16a71 71 0 0 0-6-5l-5-3c-18-11-52-11-54-11-9-12-9-51-8-60l-8 4a175 175 0 0 0-24 21 210 210 0 0 0-22 26 203 203 0 0 0-32 73c0 1-9 38-5 57z' fill='url(%23ff-h)'/%3E%3Cpath d='M341 167a130 130 0 0 1 22 29 46 46 0 0 1 4 3c55 50 26 121 24 126 44-36 72-90 64-146-27-68-73-95-111-155a255 255 0 0 1-8-14 44 44 0 0 1-4-9 1 1 0 0 0 0-1 1 1 0 0 0-1 0c-9 5-65 92 10 167z' fill='url(%23ff-i)'/%3E%3Cpath d='M367 199a46 46 0 0 0-4-3l-1-1c-13-9-36-18-58-15 86 44 63 193-57 187a107 107 0 0 1-31-6 131 131 0 0 1-11-5c17 12 99 39 186-31 2-5 31-76-24-126z' fill='url(%23ff-j)'/%3E%3Cpath d='M148 277s12-41 80-41c7 0 28-20 29-26s-44 18-90-4c-51-24-89 4-89 4s15 35 57 35c-4 40 16 85 67 110l3 1c-29-15-54-44-57-79z' fill='url(%23ff-k)'/%3E%3Cpath d='M479 166c-11-25-32-52-49-60a249 249 0 0 1 25 73c-27-68-73-95-111-155a255 255 0 0 1-8-14 44 44 0 0 1-4-9 1 1 0 0 0 0-1 1 1 0 0 0-1 0c-60 35-81 101-83 134l9-1c45 0 84 25 105 62-13-9-36-18-58-14 86 43 63 192-57 186a107 107 0 0 1-31-6 131 131 0 0 1-11-5l-3-1 3 1c-29-15-54-44-57-79 0 0 12-41 80-41 7 0 28-20 29-26 0-2-42-19-58-35l-17-16a71 71 0 0 0-6-5 111 111 0 0 1-1-58c-25 11-44 29-58 44-9-12-9-52-8-60l-8 4a175 175 0 0 0-24 21 210 210 0 0 0-22 26 203 203 0 0 0-32 73l-1 2-2 15a279 279 0 0 0-4 34v1a240 240 0 0 0 477 40l1-9c5-41 0-84-15-121zm-24 13z' fill='url(%23ff-l)'/%3E%3C/svg%3E)
- ' xlink:href='%23s-b'%3E%3Cstop offset='0' stop-color='%2324a5f3' stop-opacity='0' /%3E%3Cstop offset='1' stop-color='%231e8ceb' /%3E%3C/radialGradient%3E%3CradialGradient id='s-j' cx='109.3' cy='13.8' r='93.1' gradientTransform='matrix(-.02 1.1 -1.04 -.02 137 -115)' xlink:href='%23s-b'%3E%3Cstop offset='0' stop-opacity='0' /%3E%3Cstop offset='1' stop-color='%235488d6' stop-opacity='0' /%3E%3Cstop offset='1' stop-color='%235d96eb' /%3E%3C/radialGradient%3E%3C/defs%3E%3Crect width='220' height='220' x='22' y='-107' fill='url(%23s-a)' ry='49' transform='matrix(.57 0 0 .57 187 256)' /%3E%3Cg transform='translate(194 190)'%3E%3Ccircle cx='67.8' cy='67.7' fill='url(%23s-c)' paint-order='stroke fill markers' r='54' /%3E%3Ccircle cx='-69.9' cy='69.3' fill='url(%23s-i)' transform='translate(138 -2)' r='54' /%3E%3C/g%3E%3Cellipse cx='120' cy='14.2' fill='url(%23s-j)' rx='93.1' ry='93.7' transform='matrix(.58 0 0 .58 192 250)' /%3E%3Cg transform='matrix(.58 0 0 .57 197 182)'%3E%3Cpath fill='%23cac7c8' d='M46 192h1l72-48-7-9-66 57Z' /%3E%3Cpath fill='%23fbfffc' d='M46 191v1l66-57-7-9-59 65Z' /%3E%3Cpath fill='url(%23s-d)' d='m119 144-7-9 66-57-59 66Z' /%3E%3Cpath fill='%23fb645c' d='m105 126 7 9 66-57-1-1-72 49Z' /%3E%3C/g%3E%3Cpath stroke='%23fff' stroke-linecap='round' stroke-miterlimit='1' stroke-width='1.3' d='m287 278 3-2m-12-17 8-2m-8-3h4m-4-13 8 2m-8 3h4m-1-13 7 3m-4-11 7 4m-2-11 6 6m0-12 6 7m1-11 4 6m4-10 3 7m5-9 2 7m15-7-1 7m10-5-3 7m11-4-4 7m11-2-5 6m16 7-7 4m10 4-7 3m10 6-8 1m8 16-8-2m5 10-7-3m4 11-7-4m2 11-6-5m0 11-5-6m-2 11-4-7m-4 11-3-8m-6 10-1-8m-16 8 2-8m-10 5 3-7m-11 4 4-7m-11 2 5-6m-8 3 3-3m4 8 2-3m5 8 2-4m6 7 1-4m8 5v-4m8 4v-4m9 3-1-4m9 1-2-4m9 0-2-4m9-2-3-3m8-4-3-2m8-5-4-2m7-6-4-1m5-8h-4m4-8h-4m3-9-4 1m1-9-4 2m-1-9-3 2m-2-9-3 3m-4-8-2 3m-5-8-2 4m-6-6-1 3m-8-5v4m-8-4v4m-9-2 1 3m-9 0 2 3m-9 1 2 3m-9 2 3 3m-8 4 3 2m-8 5 4 2m-7 6 4 1m-4 25 4-1m-2 5 7-3m-6 7 4-2m-2 6 7-4m-13-21h8m41-41v-8m0 99v-8m49-42h-8' transform='translate(-65 8)' /%3E%3C/svg%3E)
[Source](https://developer.mozilla.org/docs/Web/API/StorageManager/persisted)
To learn more about eviction, how much you can store, and how to handle quota
limitations, see [Storage for the web](https://web.dev/articles/storage-for-the-web).
## Check if your site's storage has been marked as persistent
You can use JavaScript to determine if your site's storage has been marked
as persistent. Calling `navigator.storage.persisted()` returns a Promise that
resolves with a boolean, indicating whether storage has been marked as
persisted.
// Check if site's storage has been marked as persistent
if (navigator.storage && navigator.storage.persist) {
const isPersisted = await navigator.storage.persisted();
console.log(`Persisted storage granted: ${isPersisted}`);
}
## When should I ask for persistent storage?
The best time to request your storage be marked as persistent is when you
save critical user data, and the request should ideally be wrapped in a user
gesture. Do not ask for persistent storage on page load, or in other bootstrap
code, the browser may prompt the user for permission. If the user
isn't doing anything that they think needs to be saved, the prompt may be
confusing, and they'll likely reject the request. Additionally, don't prompt
too frequently. If the user decided not to grant permission, don't immediately
prompt again on the next save.
## Request persistent storage
To request persistent storage for your site's data, call
`navigator.storage.persist()`. It returns a Promise that resolves with a
boolean, indicating whether the persistent storage permission was granted.
// Request persistent storage for site
if (navigator.storage && navigator.storage.persist) {
const isPersisted = await navigator.storage.persist();
console.log(`Persisted storage granted: ${isPersisted}`);
}
> [!NOTE]
> **Note:** The API names to *check* if your site's storage has already been marked persistent, and to *request* persistent storage are very similar. The way I remember the difference is `persisted()` is past-tense, and is used to check if it's already persist**ed** . Whereas `persist()` is present-tense and asks for it now.
### How is permission granted?
Persistent storage is treated as a [permission](https://storage.spec.whatwg.org/#persistence). Browsers use
different factors to decide whether to grant persistent storage permissions.
#### Chrome and other Chromium-based browsers
Chrome, and most other Chromium-based browsers automatically handle the
permission request, and do not show any prompts to the user. Instead, if a
site is considered important, the persistent storage permission is
automatically granted, otherwise it is silently denied.
The heuristics to determine if a site is important include:
- How high is the level of site engagement?
- Has the site been installed or bookmarked?
- Has the site been granted permission to show notifications?
If the request was denied, it can be requested again later and will be
evaluated using the same heuristics.
#### Firefox
Firefox delegates the permission request to the user. When persistent storage
is requested, it prompts the user with a UI popup asking if they will allow
the site to store data in persistent storage.
 A popup shown by Firefox when a site requests persistent storage.
## What storage is protected by persistent storage?
If the persistent storage permission is granted, the browser won't evict
data stored in:
- Cache API
- Cookies
- DOM Storage (Local Storage)
- File System API (browser-provided and sandboxed file system)
- IndexedDB
- Service workers
- App Cache (deprecated, don't use)
- WebSQL (deprecated, don't use)
## How to turn off persistent storage
At this time, there is no programmatic way to tell the browser you no longer
need persistent storage.
## Conclusion
Research from the Chrome team shows that although possible, stored data is
rarely cleared automatically by Chrome. To protect critical data that may
not be stored in the cloud, or will result in significant data loss,
persistent storage can be a helpful tool to ensure that your data is not
removed by the browser when the local device is faced with storage pressure.
And remember, only request persistent storage when the user is most likely to
want it.
### Thanks
Special thanks to Victor Costan, and Joe Medley for reviewing this document.
Thanks to Chris Wilson who wrote the original version of this document that
first appeared on WebFundamentals.