fluffos/docs/efun/jsbridge/js_export.md

title
jsbridge / js_export

js_export

NAME

js_export - register an LPC function the hosting page can call

SYNOPSIS

int js_export(string name);                              // unregister
int js_export(string name, string | function callback);  // register

DESCRIPTION

Registers `callback` under `name` so the page's JavaScript can call
into LPC:

    // JS (Promise of the string result)
    const sum = await Module.fluffos.callLPC("add", "2", "3");

The callback runs on the next driver tick (proper driver context,
like call_out) as:

    mixed callback(string *args, int id);

`args` are the JavaScript arguments as strings; `id` is the call id.
The return value settles the page's Promise: a string is passed
through as-is, other values are %O-formatted (integers and floats
print plainly; return a JSON-encoded string for structured data). A
runtime error in the callback, or a destructed owner object, rejects
the Promise.

A string callback names a function called on the registering object.
Re-registering a name replaces the previous entry; calling with only
`name` unregisters it. Returns 1 when a callback was registered, 0
when the name was (or is now) unregistered.

Like call_out(1), the callback runs without a command context:
this_player() is 0 inside it.

Only available on the WebAssembly build (guard LPC code with
`#ifdef __PACKAGE_JSBRIDGE__`).

EXAMPLES

```c
private mixed lpc_add(string *args, int id) {
    int total = 0;
    foreach (string a in args) total += to_int(a);
    return total;
}

void create() { js_export("add", (: lpc_add :)); }
```

Page side (helper included in the bundled web shell):
```js
const sum = await fluffos.callLPC("add", "2", "3");   // "5"
```

SEE ALSO

js_call(3), js_eval(3), call_out(3)

NOTE

Exports are driver-global (one namespace per driver instance) and
hold a reference on the registering object until unregistered. The
page can only call names the mudlib chose to export -- the export
table is the mudlib's capability surface toward the page, the mirror
of the page's handler table.