# How to extend index from hooks?
**URL:** https://community.silverbullet.md/t/how-to-extend-index-from-hooks/3060
**Category:** Lua
**Created:** [August 20, 2025, 1:38pm UTC](https://community.silverbullet.md/t/how-to-extend-index-from-hooks/3060 "2025-08-20T13:38:32Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@mjf](https://community.silverbullet.md/u/mjf)
#### Post date: [August 20, 2025, 1:38pm UTC](https://community.silverbullet.md/t/how-to-extend-index-from-hooks/3060/1 "2025-08-20T13:38:32Z")
Does any way exist to extend the index from appropriate hooks?
_TL;DR_
I am trying to extend index for pages with custom value. I dully hoped the following will work (intuitively):
````lua
```space-lua
event.listen {
name = 'editor:pageSaved',
run = function(e)
e.testingVariable = e.lastModified
print('Data', e.data)
return e
end
}
```
````
It seems the `e` is immutable or something because the `print()` call does not print the `testingVariable` at all.
---
### Author:  [@zef](https://community.silverbullet.md/u/zef)
#### Post date: [August 20, 2025, 1:41pm UTC](https://community.silverbullet.md/t/how-to-extend-index-from-hooks/3060/2 "2025-08-20T13:41:32Z")
You cannot extend page attributes, but you could create separate objects as part of the index process. The event to listen to is `page:index`.
You can then create new objects via the `index.indexObjects` API: [API/index](https://silverbullet.md/API/index#index.indexObjects(page,%20objects))
---
### Author:  [@mjf](https://community.silverbullet.md/u/mjf)
#### Post date: [August 21, 2025, 5:31am UTC](https://community.silverbullet.md/t/how-to-extend-index-from-hooks/3060/3 "2025-08-21T05:31:10Z")
OK, I will give it a try. But still, if the `e` in my example above is immutable, I should at least see some warning(s) in the console (which I don’t).
---
### Author:  [@zef](https://community.silverbullet.md/u/zef)
#### Post date: [August 21, 2025, 8:41am UTC](https://community.silverbullet.md/t/how-to-extend-index-from-hooks/3060/4 "2025-08-21T08:41:41Z")
There isn’t really such a thing as immutable data in Lua
---
### Author:  [@mjf](https://community.silverbullet.md/u/mjf)
#### Post date: [August 21, 2025, 11:13am UTC](https://community.silverbullet.md/t/how-to-extend-index-from-hooks/3060/5 "2025-08-21T11:13:04Z")
OOPS! My fault, there’s a typo in the code. 😉
> There isn’t really such a thing as immutable data in Lua
_TL;DR_
To explain more further… One can always play with table’s metamethods to gain _poor man’s_ sort of “immutability” as some sort of “safety net” (if needed)…
```lua
function immutable(tbl)
return setmetatable({}, {
__index = tbl,
__newindex = function(tbl, key, val)
error('Cannot modify read-only table')
end,
__metatable = false
})
end
local t = immutable { x = 1, y = 2, z = 3 } -- new "immutable" table `t`
```
It’s a nice trick but **MUST NOT** be considered as a “security feature” or something like that because the `rawset()` call can still be used to override this!
So, yes, there is simply **no real immutability in Lua**. 🙂