How/Where to store data in a Chrome Tampermonkey script?

Question

I wrote one Greasemonkey/Tampermonkey script for Facebook . I needed to store data to retrieve it later. For that I used localStorage.
That was working fine. But I noticed that after few hours all data which I stored was removed automagicllay. Probably Facebook itself deletes all localStorage data.

Now, I searched for alternatives.

1. Cookies : No this will be removed when user clears history.
2. Web SQL : Apparently it is dropped by w3.org. So in near future I assume chrome might not be using web sql too.

I want to store the data in client system. What option do I have? Should I use FileSystem to store data?

Answer 1

Since you are using Tampermonkey (Chrome) and Greasemonkey (Firefox). Go ahead and use GM_setValue(). It cannot be cleared by Facebook or by any other website.

It has the advantage of storing values cross-domain, as well.

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Beware that the bog-standard GM_setValue() is somewhat problematic on Firefox. It can cause a script instance to crash on invalid values -- So it's best to use a serializer, such as GM_SuperValue, to store anything but strings. Even innocent-looking integers can cause the default GM_setValue() to crash.

Currently, only GM_setValue(), cookies, localStorage, and IndexedDB are available for persistent data on both browsers.

IndexedDB would also probably do what you want, but it is nowhere as easy to use as GM_setValue().

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Update:
Nowadays, don't forget to use:

• // @grant GM_setValue
  and
• // @grant GM_getValue

Also, if you do use the GM_SuperValue library, you would now add it with:

// @require http://userscripts-mirror.org/scripts/source/107941.user.js 

in the metadata block. (Since userscripts.org is long dead.)