获取promise 状态

function promiseState(p) {
  const t = {};
  return Promise.race([p, t])
    .then(v => (v === t)? "pending" : "fulfilled", () => "rejected");
}

var a = Promise.resolve();
var b = Promise.reject();
var c = new Promise(() => {});

promiseState(a).then(state => console.log(state)); // fulfilled
promiseState(b).then(state => console.log(state)); // rejected
promiseState(c).then(state => console.log(state)); // pending