#Callbacks

Accept a JS function as a parameter using napi.Callback. The argument is validated on conversion: passing a non-function throws TypeError before your code runs.

pub fn forEach(env: napi.Env, items: []napi.Val, cb: napi.Callback) !void {
    for (items, 0..) |item, i| {
        _ = try cb.call(env, .{ item, @as(u32, @intCast(i)) });
    }
}

addon.forEach([10, 20, 30], (item, i) => console.log(i, item));
// 0 10
// 1 20
// 2 30

#call(env, args_tuple)

call's second argument is a Zig tuple. Each element is auto-converted to JS. The call uses undefined as this.

_ = try cb.call(env, .{ 1, "hello", true });

You can also pass a []const Val slice when you have one already built:

const argv: []const napi.Val = ...;
_ = try cb.call(env, argv);

The return value of call is a napi.Val. Convert it to a Zig type with .to(env, T):

const result = try cb.call(env, .{42});
const n = try result.to(env, i32);

#callWith(env, this, args)

For a specific this binding:

pub fn invokeOn(env: napi.Env, target: napi.Val, cb: napi.Callback) !napi.Val {
    return cb.callWith(env, target, .{});
}

addon.invokeOn(obj, function () {
  return this.x;
});

#Cross-thread: threadsafe(env, name, T)

Calling cb.call from a non-main thread crashes Node. To call back into JS from a worker thread, wrap the callback as a ThreadsafeFn:

const tsfn = try cb.threadsafe(env, "events", u32);

The third argument is the per-call payload type. Use void for signal-only callbacks. See Threadsafe functions for the full pattern.

#Method summary