promise.all返回的是新的promise 其中.then的结果是所有promise被处理好之后的结果 需要注意promise的结果不能直接push，因为顺序可能是异步的 ```js function pAll(arr) { let allRes = []; let count = 0; return new Promise((resolve, reject) => { arr.forEach((promise, i) => { promise.then( (res) => { count++; allRes[i] = res; if (count === arr.length) { resolve(allRes); } }, (err) => { reject(err); } ); }); }); } let p1 = Promise.resolve(111); let p2 = Promise.resolve(222); // let p3 = Promise.all([p1, p2]) let p3 = pAll([p1, p2]); p3.then((res) => { console.log(res); }); ```