# `gno.land/r/moul/reactions/v0`
A reaction block any realm can embed, keyed on the **page** it appears on rather
than on the realm that stores it.
It is the shape the web settled on for this in 2010: one hosted widget, the same
snippet pasted everywhere, deciding what to show from the page identifier it is
handed. Here the snippet is two lines of gno.
```go
import "gno.land/r/moul/reactions/v0"
func Render(path string) string {
return body + reactions.RenderBlock()
}
```
That is the whole integration. Your realm stores nothing, registers nothing and
configures nothing, and redeploying it never loses anyone's reaction.
## Why `RenderBlock` needs no argument
A plain read exported by one realm and called by another is **borrowed**: gno
opens no realm frame for it, so `unsafe.CurrentRealm()` inside it reports the
**caller**. `RenderBlock` uses that as the page key, which is why the same line
does the right thing in every realm that pastes it. (Measured on
`gnolang/gno@master` 2026-09-22, recorded in this repo's `AGENTS.md`; it is the
same mechanism behind `r/moul/config`'s `TopBlock`.)
Adding a `cur realm` parameter would silently reverse it and key every embed to
this realm, which is exactly why there is none.
`RenderBlockFor(page)` is the explicit form: use it from a crossing function,
where there is no caller to read off the stack, or to key one block per article
on the path you already serve.
```go
return body + reactions.RenderBlockFor("gno.land/r/you/blog:" + path)
```
## What it is, and what it refuses to be
Not a comment system. There is no text field anywhere, which is what lets it run
with **no moderation at all**: a closed palette of six, one reaction per address
per page, changeable and removable. The block shows the tally and who reacted
last. That is the feature.
| key | |
|---|---|
| `up` | 👍 |
| `heart` | 💜 |
| `fire` | 🔥 |
| `party` | 🎉 |
| `rocket` | 🚀 |
| `eyes` | 👀 |
`React` aborts on anything else. That is the entire content policy, and it is a
compile-time constant rather than a list someone has to curate.
## The surface
| | |
|---|---|
| `React(cur, page, key)` | record the caller's reaction. Reacting again with a different key moves it; with the same key it only updates the "last reaction" line |
| `Unreact(cur, page)` | remove it. Aborts when there is none, rather than succeeding silently |
| `RenderBlock()` | the embed, keyed on the calling realm |
| `RenderBlockFor(page)` | the embed for a named page |
| `Count` · `CountOf` · `ReactionOf` · `Last` · `Pages` | reads, for a host realm that wants the numbers without the markdown |
`Render("")` is the getting-started page plus the board;
`Render("<page>")` is one page's tally, which is where the link under every
block goes.
## Two things that are permanent, and were decided on purpose
**This realm is public, so it can never be redeployed.** A private realm cannot
be imported at all, and being imported is the entire feature. The redeploy that
`private = true` would have bought is given up deliberately: the tallies under
this path belong to everyone who reacted, not to the deployer, and a redeploy
wipes every package-level variable. A fix ships as a `v1` beside this one that
keeps reading it, never as a replacement.
**The page key is not checked against anything.** A page is just a name: nothing
verifies that the realm exists, that it embeds the block, or that the caller has
any relationship to it. That is what lets a realm key the block on something
finer than itself, and it means the board index is an open list. The index is
capped at 25 rows for that reason; every page keeps its own view regardless.
## Not to be confused with
[`r/moul/x/daily/reactions`](https://github.com/moul/gno-contracts/tree/main/r/moul/x/daily/reactions)
is an older, unrelated experiment: a single self-contained board with its own
"topics", no embedding, and no way for a reader to change or remove a reaction.
Nothing is shared between the two.
## Where the code is
The engine (pages, tallies, palette, the block markdown) is
[`p/moul/reactions/v0`](https://github.com/moul/gno-contracts/tree/main/p/moul/reactions).
This realm is the authority half: who may write, what the chain says the height
and the caller are, and the two views.
First host: [`r/moul/home`](https://github.com/moul/gno-contracts/tree/main/r/moul/home),
which renders it as a `:reactions:` layout placeholder.
<!-- BEGIN GNOCONTRACTS FOOTER (generated by `make readmes`; do not edit below) -->
---
Part of **[moul/gno-contracts](https://github.com/moul/gno-contracts)** — moul's versioned gno.land contracts. See the repository for the full catalog, build/test tooling, and usage.
**Dependency graph:**
> ⚠️ **Disclaimer:** provided as-is, without warranty; not security-audited. Full disclaimer: [DISCLAIMER](https://github.com/moul/gno-contracts/blob/main/DISCLAIMER.md).
<!-- END GNOCONTRACTS FOOTER -->
Count(page string) int
CountOf(page string, key string) int
Last(page string) (key string, who string, height int64)
Pages() int
React(cur interface {.seal func(); Address func() .uverse.address; IsCode func() bool; IsCurrent func() bool; IsEphemeral func() bool; IsUser func() bool; IsUserCall func() bool; IsUserRun func() bool; PkgPath func() string; Previous func() .uverse.realm; String func() string; Sub func(string) .uverse.realm; Subpath func() string}, page string, key string)
ReactionOf(page string, who string) string
Render(path string) string
RenderBlock() string
RenderBlockFor(page string) string
Unreact(cur interface {.seal func(); Address func() .uverse.address; IsCode func() bool; IsCurrent func() bool; IsEphemeral func() bool; IsUser func() bool; IsUserCall func() bool; IsUserRun func() bool; PkgPath func() string; Previous func() .uverse.realm; String func() string; Sub func(string) .uverse.realm; Subpath func() string}, page string)
Signatures reconstructed verbatim from vm/qfuncs — interface params keep their inline definitions.
vm/qrender output, sanitized (docs/render-security.md) and displayed in an empty-sandbox iframe — scripts, forms and popups cannot run. Links stay inert in-preview; right-click to open.