Measure cost of async in node

Measure cost of async in node.js

// node --expose-gc script.js


global.gc(true);
const before = process.memoryUsage().heapUsed;

const arr = [];
const count = 1 * 1024 * 1024;
const never = new Promise(() => {});

for (let i = 0; i < count; i++) {
  arr.push(foo(i));
}

async function foo(i) {
  // I want to measure the cost of an unresolved async function
  await never;
  // Make sure `i` is captured into the async state
  console.log(i);
}

global.gc(true);
const after = process.memoryUsage().heapUsed;

// On my machine: "Uses 421 bytes per async function"
console.log(`Uses ${Math.round((after - before) / count)} bytes per async function`)