var p = function () {
  return new Promise(function (resolve, reject) {
    setTimeout(() => {
      console.log("1000");
      resolve();
    }, 1000);
  });
};
var p1 = function () {
  return new Promise(function (resolve, reject) {
    setTimeout(() => {
      console.log("2000");
      resolve();
    }, 2000);
  });
};
var p2 = function () {
  return new Promise(function (resolve, reject) {
    setTimeout(() => {
      console.log("3000");
      resolve();
    }, 3000);
  });
};

p()
  .then(() => {
    return p1();
  })
  .then(() => {
    return p2();
  })
  .then(() => {
    console.log("end");
  });

Promise.all((promises: [])).then((fun: function));

var promises = function () {
  return [1000, 2000, 3000].map((current) => {
    return new Promise(function (resolve, reject) {
      setTimeout(() => {
        console.log(current);
      }, current);
    });
  });
};

Promise.all(promises()).then(() => {
  console.log("end");
});

function multiRequest(urls, maxNum) {
 const len = urls.length; // 請(qǐng)求總數(shù)量
 const res = new Array(len).fill(0); // 請(qǐng)求結(jié)果數(shù)組
 let sendCount = 0; // 已發(fā)送的請(qǐng)求數(shù)量
 let finishCount = 0; // 已完成的請(qǐng)求數(shù)量
 return new Promise((resolve, reject) => {
     // 首先發(fā)送 maxNum 個(gè)請(qǐng)求，注意：請(qǐng)求數(shù)可能小于 maxNum，所以也要滿足條件2
     // 同步的 創(chuàng)建maxNum個(gè)next并行請(qǐng)求 然后才去執(zhí)行異步的fetch 所以一上來(lái)就有5個(gè)next并行執(zhí)行
     while (sendCount < maxNum && sendCount < len) { 
         next();
     }
     function next () {
         let current = sendCount ++; // 當(dāng)前發(fā)送的請(qǐng)求數(shù)量，后加一 保存當(dāng)前請(qǐng)求url的位置
         // 遞歸出口
         if (finishCount >= len) { 
         // 如果所有請(qǐng)求完成，則解決掉 Promise，終止遞歸
             resolve(res);
             return;
         }
         const url = urls[current];
         fetch(url).then(result => {
             finishCount ++;
             res[current] = result;
             if (current < len) { // 如果請(qǐng)求沒(méi)有發(fā)送完，繼續(xù)發(fā)送請(qǐng)求
                 next();
             }
         }, err => {
             finishCount ++;
             res[current] = err;
             if (current < len) { // 如果請(qǐng)求沒(méi)有發(fā)送完，繼續(xù)發(fā)送請(qǐng)求
                 next();
             }
         });
     }
 });
}