[JavaScript知识库]js Promise

      new Promise(function(resolve, reject){
        setTimeout(() => {
          console.log("first");
          resolve();
        }, 1000);
      }).then(function(){
        return new Promise(function(resolve, reject){
          setTimeout(() => {
            console.log("second");
            resolve();
          }, 4000);
        })
      }).then(function(){
        setTimeout(() => {
          console.log("third");
        }, 3000);
      })

简化

//-----------------简化---------------------------------
      function print(delay, message){
        return new Promise(function(resolve, reject){
          setTimeout(() => {
            console.log(message);
            resolve();
          }, delay);
        })
      }

      print(1000, 'first').then(function(){
        return print(2000, 'second');
      }).then(function(){
        print(0, 'third');
        throw "an error"; 
      }).catch(function(error){
        console.log(error);
      })

//----------------------async/await----------------
      async function asyncFunc(){
        await print(1000, 'first');
        await print(2000, 'second');
        await print(1000, 'third');
      }

      asyncFunc();

//-------------------async/await/catch-----------------------
      async function asyncFunc() {
          try {
              let res = await new Promise(function (resolve, reject) {
                  resolve("2222");
                  // throw "Some error"; // 或者 reject("Some error")
              });
              console.log(res);
          } catch (err) {
              console.log(err);
              // 会输出 Some error
          }
      }
      asyncFunc();

//----------------Promise.all()--------------------------
      let promises = [2,3,4,5,6].map(function(id){
        return "/post/"+id+".json";
      })
      Promise.all(promises).then(function(posts){
        console.log(posts);
      }).catch(function(error){
        console.log(error);
      })

//-------------------Promise.resolve()-----------------------
      var p = Promise.resolve('hihihi');
      p.then(function(s){
        console.log(s);
      })

      //-------------------Promise.reject()-----------------------
      var p = Promise.reject('出错了.');
      p.then(null, function(s){
        // console.log(s);
      })