a.js

const _a = fA();
const _b = fB();
const _c = fC();
const _d = Promise.all([_a, _b]).then(([a, b]) => fD(a, b));
const _e = Promise.all([_b, _c]).then(([b, c]) => fE(b, c));
const [d, e] = await Promise.all([_d, _e]);
const f = await fF(d, e);