hello.rs

fn main() {}

#[no_mangle]
pub fn add_one(x: i32) -> i32 {
  x + 1
}

run.js

const fs = require('fs');
const buf = fs.readFileSync('./hello.wasm');
var m = new WebAssembly.Instance(new WebAssembly.Module(buf));
var h = new Uint8Array(m.exports.memory.buffer);
var p = m.exports.add_one(3);
console.log(p)

$ rustc +nightly --target wasm32-unknown-unknown -O hello.rs
$ node --expose-wasm run.js
4