index.js

var addon = require('../native');

var array1 = new Uint8Array([0, 1, 2, 3, 4, 5, 6, 7]);
var array2 = new Uint8Array(addon.munge(array1.buffer));
console.log(array1);
console.log(array2);

lib.rs

use neon::js::binary::JsArrayBuffer;

fn munge(call: Call) -> JsResult<JsArrayBuffer> {
    let scope = call.scope;
    let mut buffer = call.arguments.require(scope, 0)?.check::<JsArrayBuffer>()?;
    buffer.grab(|mut contents| {
        // modify the input buffer
        contents[0] = 42;
    });
    // return a new buffer
    JsArrayBuffer::new(16)
}

register_module!(m, {
    m.export("munge", munge)
});