#class

pub const MyClass = napi.class("MyClass", struct { ... });

Wrap a Zig struct as a JS class. The first argument is the JS-visible class name; the second is the Zig type.

pub const Counter = napi.class("Counter", struct {
    value: i32,

    pub fn init(start: i32) @This() {
        return .{ .value = start };
    }

    pub fn increment(self: *@This()) i32 {
        self.value += 1;
        return self.value;
    }

    pub fn deinit(self: *@This()) void {
        _ = self;
    }
});

const c = new Counter(10);
c.increment(); // 11

For the conceptual model, see Classes.

#Recognized members

init may also return !T to make construction fallible. Env is recognized in the constructor's first slot and any method's second slot, and does not consume a JS argument.

A next taking only self (plus optional Env) and returning an optional (or !?Item) makes instances iterable: they work with for..of, spread, and Array.from, and the generated .d.ts declares [Symbol.iterator](): IterableIterator<Item>. next is still exposed as a regular method. See Classes › Iterators.

#Allocation

The instance is heap-allocated once (on std.heap.smp_allocator) during new and reused across every method call. Released automatically when JS collects the wrapper, after running deinit if defined.

If your fields hold long-lived allocations (strings, slices, file handles), free them in deinit. The arena from env.allocator() is per-call only and is not suitable for instance state.