js promise. all

let d= promise.all（[a,b,c]）

Accept one promise Array , Only those in the array promise Success returns only after all success , Or fail

Only a、b、c The state of fulfilled,d The state of fulfilled, here a、b、c The return value of consists of an array , Pass to d Callback function for .
as long as a、b、c One of them was rejected,d The state of rejected, At this time, the first was reject The return value of the instance of , Will pass to p Callback function for .

Interview questions

function c In function a and b Only after the execution

Just use promise.all

let a=function(){
        console.log('a')
    }
    let b=function(){
        console.log('b')
    }
        
        let p1 = new Promise((resolve, reject) => {
            a()
             resolve(' succeed ')
        })
        
        let p2 = new Promise((resolve, reject) => {
              b()
          resolve('success')
        })
        
        let c=function(){
            console.log('c')
        }
        
        Promise.all([p1, p2]).then((result) => {
            c()
        })