JavaScript中Promise函数执行顺序

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Promise的执行顺序记录：

前言：Javascript执行环境是单线程的，也就是说JS环境中负责解释和执行的线程只有一个；那么Promise函数在JavaScript中执行时的顺序（纸上得来终觉浅）！

D级：

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`)
    }   //-->运行结果是 console 1；console 2；console 3；console 4；console 6

 

C级：

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级：

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级：

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级：

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

 

简单小结：在一个函数中执行顺序-->已申明的函数-->new Promise-->setTimeout；在Promise函数中后执行.then()函数；

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