node.js Promise对象的使用方法实例分析

let flag = true;
const hello = new Promise(function (resolve, reject) {
  if (false) {//异步操作成功
    resolve("success");
  } else {
    reject("error");
  }
});

hello.then(
  function (value) {
    console.log(value)
  },
  function (err) {
    console.log(err)
  }
);

function chenqionghe(second) {
  return new Promise((resolve, reject) => {
    setTimeout(function () {
      console.log("chenqionghe");
      resolve();
    }, second * 1000);
  })
}
function get(second) {
  return new Promise((resolve, reject) => {
    setTimeout(function () {
      console.log("get");
      resolve()
    }, second * 1000);
  })
}
function muscle(second) {
  return new Promise((resolve, reject) => {
    setTimeout(function () {
      console.log("muscle");
      resolve();
    }, second * 1000);
  })
}

chenqionghe(3)
  .then(function () {
    return get(2)
  })
  .then(function () {
    return muscle(1)
  });

chenqionghe(3);
get(2);
muscle(1);

chenqionghe(3)
  .then(function () {
    return get(2)
  })
  .then(function () {
    throw new Error("abc");
    return muscle(1)
  })
  .catch(function (e) {
    console.log("异常:" + e.message)
  })
;

chenqionghe(3)
  .then(function () {
    return get(2)
  })
  .then(function () {
    throw new Error("abc");
    return muscle(1)
  })
  .catch(function (e) {
    console.log("异常:" + e.message)
  })
  .then(function () {
    console.log("异常后执行")
  })
;

chenqionghe(3)
  .then(function () {
    return get(2)
  })
  .then(function () {
    throw new Error("abc");
    return muscle(1)
  })
  .catch(function (e) {
    console.log("异常:" + e.message)
  })
  .finally(function () {
    console.log("最后都会执行的方法")
  })
;

const p = Promise.all([p1, p2, p3]);

Promise.resolve('foo')
// 等价于
new Promise(resolve => resolve('foo'))

const p = Promise.reject('出错了');
// 等同于
const p = new Promise((resolve, reject) => reject('出错了'))