JavaScript中Promise函數執行順序

​

Promise的執行順序記錄：

前言：Javascript執行環境是單線程的，也就是說JS環境中負責解釋和執行的線程只有一個；那么Promise函數在JavaScript中執行時的順序（紙上得來終覺淺）！

D級：

testFunction() {
      console.log(`console 1`);
      new Promise((resolve, reject) => {
          console.log(`console 2`);
          resolve(console.log(`console 3`));
          reject(console.log(`console 4`))
      }).then().catch(() => {
          console.log(`consolve 5`)
      });
      console.log(`console 6`)
    }   //-->運行結果是 console 1；console 2；console 3；console 4；console 6

 

C級：

testFunction() {
      console.log(`console 1`);
      new Promise((resolve, reject) => {
          console.log(`console 2`);
          resolve(console.log(`console 3`));
          reject(console.log(`console 4`))
      }).then(() => {
          setTimeout(() => {
              console.log(`console 7`)
          },0)
      }).catch(() => {
          console.log(`consolve 5`)
      });
      console.log(`console 6`)
    } // -->console 1；console 2；console 3；console 4；console 6；console 7

 

B級：

testFunction() {
      console.log(`console 1`);
      new Promise((resolve, reject) => {
          console.log(`console 2`);
          resolve(console.log(`console 3`));
          reject(console.log(`console 4`))
      }).then(() => {
          setTimeout(() => {
              console.log(`console 7`);
              new Promise(() => {
                  console.log(`console 8`)
              }).then(console.log(`console 9`))
          },0)
      }).catch(() => {
          console.log(`consolve 5`)
      });
      console.log(`console 6`)
    } // -->console 1；console 2；console 3；console 4；console 6；console 7；console 8；console 9

 

A級：

testFunction() {
      console.log(`console 1`);
      setTimeout(() => {
          new Promise(() => {
              console.log(`console 10`);
          }).then(console.log(`console 11`));
      },0);
      new Promise((resolve, reject) => {
          console.log(`console 2`);
          resolve(console.log(`console 3`));
          reject(console.log(`console 4`))
      }).then(() => {
          setTimeout(() => {
              console.log(`console 7`);
              new Promise(() => {
                  console.log(`console 8`)
              }).then(console.log(`console 9`))
          },0)
      }).catch(() => {
          console.log(`consolve 5`)
      });
      console.log(`console 6`)
    }//-->console 1；console 2；console 3；console 4；console 6；console 10；console 11；console 7；console 8；console 9

 

S級：

testFunction() {
      console.log(`console 1`);
      setTimeout(() => {
          new Promise(() => {
              console.log(`console 10`);
          }).then(console.log(`console 11`));
      },0);
      let letP =new Promise(() => {
          setTimeout(() => {
              console.log(`console 12`);
          },0)
      });
      promiseFn(letP);
      function promiseFn(fn){
        console.log(`console 13`)
        return fn;
      };
      new Promise((resolve, reject) => {
          console.log(`console 2`);
          resolve(console.log(`console 3`));
          reject(console.log(`console 4`))
      }).then(() => {
          setTimeout(() => {
              console.log(`console 7`);
              new Promise(() => {
                  console.log(`console 8`)
              }).then(console.log(`console 9`))
          },0)
      }).catch(() => {
          console.log(`consolve 5`)
      });
      console.log(`console 6`)
    } //-->consolve 1；consolve 13；consolve 2；consolve 3；consolve 4；consolve 6；consolve 10；consolve 11；consolve 12；consolve 7；consolve 8；consolve 9

 

簡單小結：在一個函數中執行順序-->已申明的函數-->new Promise-->setTimeout；在Promise函數中后執行.then()函數；

​