Why is the following code executed in order 0123456

        Promise.resolve().then(() = > {  // line1
            console.log(0);             
            return Promise.resolve(4);  // line2
        }).then((res) = > {              // line3
            console.log(res)
        })

        Promise.resolve().then(() = > {  //line4
            console.log(1)
        }).then(() = > {                 // line5
            console.log(2)
        }).then(() = > {                 // line6
            console.log(3)
        }).then(() = > {                 // line7
            console.log(5)
        }).then(() = > {                 // line8
            console.log(6)})Copy the code

• The event queue is represented as [line1__,line4, P1], in which events with __ (such as line1__) are completed events. For the sake of viewing the execution process, the event queue is represented as __.

  • 1, line1 execute, then task adds event queue, then event queue [line1]
  • 2,line4 execute, then task add event queue, then event queue [line1,line4]
  • 3. If no synchronization task exists, execute the task in the event queue
  • [line1__,line4, P1] [1, 2, 3] [1, 3, 4]
  • 5, continue the execution of task queue line4, output 1, find the task line5, join the event queue, then the event queue [line1__,line4__, P1,line5]
  • [line1__,line4__,p1__,line5,p2] [line1__,line4__,p1__,line5,p2]
  • [line1__,line4__,p1__,line5__,p2,line6] [line1__,line4__,p1__,line5__,p2,line6]
  • [line1__,line4__,p1__,line5__,p2__,line6,line3] [line1__,line4__,p1__,line5__,p2__,line6,line3]
  • [line1__,line4__,p1__,line5__,p2__,line6__,line3,line7] [line1__,line4__,p1__,line5__, line6__,line3,line7]
  • [line1__,line4__,p1__,line5__,p2__,line6__,line3__,line7]
  • [line1__,line4__,p1__,line5__,p2__,line6__,line3__,line7__,line8]
  • [line1__,line4__,p1__,line5__,p2__,line6__,line3__,line7__,line8__]

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