SEQUENCE function that will call PROMISE handlers when the promises RESOLVES in the sequence they were ordered ASAP.

sequence.js

var randP = (name)=>{
  return new Promise((rs,rj) => {
    let randTime = (Math.floor(Math.random() * 6) + 1) * 500; //500 to 3000
    setTimeout(rs, randTime, name + ' ' + randTime);
  });
};
var log = function(x){console.log(x)};

function thenLog(p){return p.then(log);}
var a = randP('1'); var b = randP('2'); var c = randP('3');

thenLog(a)
  .then(()=>
    thenLog(b)
      .then(()=>
        thenLog(c)
        )
        
//OR same thing with reduce
[a,b,c].reduce((p,c)=>{
  return p.then(()=>thenLog(c))
}, Promise.resolve())
        

sequenceFunc.js

/**
 * function that will call promise handlers when the promises resolves in the sequence they were ordered ASAP.
 *
 * @param pArr [Promise]
 * @param callsArr [Function]
 */
function sequence(pArr, callsArr){
  let callsStack = callsArr.map(c=> {
      return {
        called: false,
        val: undefined,
        call(){
          if(!this.called){
            this.called = true;
            c(this.val)
          }
        }
      };
    }
  );

  function callSeq() {
    for (let i = 0; i < callsStack.length; i++) {
      let c = callsStack[i];
      if (c.val === undefined) {break;} //if need to support non-returning promises use 'fulfilled' flag
      c.call();
    }
  }

  pArr.map((p, i)=> {
    p.then(val=> {
      callsStack[i].val = val;
      callSeq();
    })
  });
}

// usage example

var randP = (name)=>{
  return new Promise((rs,rj) => {
    let randTime = (Math.floor(Math.random() * 6) + 1) * 500; //500 to 3000
    setTimeout(rs, randTime, name + ' ' + randTime);
  });
};

var log = function(x){console.log(x)};

sequence([randP('a'),randP('b'),randP('c')], [log,log,log]);
// => will always log 'a' 'b' 'c' asap