仅按需运行循环的第二次迭代

Question

I have 2 loops, the first loop is a very short loop and run very fast and the second loop is a long loop and takes much more time.

I am passing info from the first loop into the second loop, and when the second loop finishes it will call "finish", and it needs to then trigger the first loop to run its second iteration,it will pass the second iteration info into the second loop again, and when the second loop finishes again, it will call finish" then trigger the first loop to run the third iteration.

And the process continues until the first loop finishes all its iteration.

How would i approach it? I have tried the below but it stops after the first iteration for the first loop. I just need the loop to stop after each iteration and when ondemand(a trigger) it will go to the next iteration.

 for (var i=0; i<from.length; i++) {
 if (loopfinished=true){
  }}

Or maybe run it in a different way but i am not sure if it is possible or not.

basically I will have different users which i have to run in a loop, also loop through messages for each person. But i have to wait til the message loop is completed before iterate to the next person, because i have to set sessionstorage for the person's message, if it doesn't wait for the message loop to complete, then it won't save to the correct person.

   var people=["user1@server","user2@server","user3@server"]

   // function to loop through messages for each person 
     for (var i=0; i<from.length; i++) {
    //load all the info here, when complete it will call done
    if(done){
    // when completed first person set people[2], when people[2] is done run people[3]
    }
    }

Edit

       var messageno=0;  
       var loopfinished=true; 
    var from=["user1@server","user2@server","user3@server"]
     for (var i=0; i<from.length; i++) {
     if (loopfinished){
      console.log(from[i]); 

var person=from[i]
connection.mam.query(jid, {
  "with": person,"before": '',"max":"10",
    },onMessage: function(message) {
 var message ="<div id=log2><br>'"+msg_data.message+"'</div>"

     messageno= messageno+1;
      console.log( messageno);


       if(messageno==count){
                 loopfinished=true;
      console.log("Inner loop completed");
           console.log(loopfinished);
      }
    return true;
}}

Edit Strophe RSM plugin

(function (root, factory) {
    if (typeof define === 'function' && define.amd) {
        // AMD. Register as an anonymous module.
        define("strophe.rsm", [
            "strophe"
        ], function (Strophe) {
            factory(
                Strophe.Strophe,
                Strophe.$build,
                Strophe.$iq ,
                Strophe.$msg,
                Strophe.$pres
            );
            return Strophe;
        });
    } else {
        // Browser globals
        factory(
            root.Strophe,
            root.$build,
            root.$iq ,
            root.$msg,
            root.$pres
        );

    }
}(this, function (Strophe, $build, $iq, $msg, $pres) {

Strophe.addNamespace('RSM', 'http://jabber.org/protocol/rsm');

Strophe.RSM = function(options) {
  this.attribs = ['max', 'first', 'last', 'after', 'before', 'index', 'count'];


  if (typeof options.xml != 'undefined') {

    this.fromXMLElement(options.xml);
  } else {
    for (var ii = 0; ii < this.attribs.length; ii++) {
      var attrib = this.attribs[ii];
      this[attrib] = options[attrib];
       console.log("done5");   
    }

  }
};

Strophe.RSM.prototype = {
  toXML: function() {
    var xml = $build('set', {xmlns: Strophe.NS.RSM});
    for (var ii = 0; ii < this.attribs.length; ii++) {

      var attrib = this.attribs[ii];
      if (typeof this[attrib] != 'undefined') {
        xml = xml.c(attrib).t(this[attrib].toString()).up();
        console.log("done6");
      }

    }
    return xml.tree();

  },

  next: function(max) {
    var newSet = new Strophe.RSM({max: max, after: this.last});
    return newSet;

  },

  previous: function(max) {
    var newSet = new Strophe.RSM({max: max, before: this.first});
    return newSet;

  },

  fromXMLElement: function(xmlElement) {
    for (var ii = 0; ii < this.attribs.length; ii++) {

      var attrib = this.attribs[ii];
      var elem = xmlElement.getElementsByTagName(attrib)[0];
      if (typeof elem != 'undefined' && elem !== null) {

        this[attrib] = Strophe.getText(elem);
        if (attrib == 'first') {
            console.log("done6");  
          this.index = elem.getAttribute('index');
        }

      }

    }

  }
};
}));

Answer 1

As i understand, your query call issues an async operation, and you can't get the result in the same call context which issues the request.

The onMessage event will fire only when your loop is ended, so you need to provide a means to handle the context in the callback itself.

Also if you issue all the asynchronous requests inside a loop you can't infer the order in which the operations finish.

var count = users.length;
for (var u in users)
{
 var user = users[u];
 query({onMessage:(function(user){return function(message){
   count --;
   processUserMessage(user, message); // some operation on a user and a message
   if (count === 0)
      allFinished();   
 };})(user)});
}
// At this point, none of the requests have returned. They will start arriving later.

If you need a strict order, then you have to issue the requests one by one, but not in a loop, but the next request should be issued in the previous request's callback.

var processChunk = function(user)
{
   query({onMessage:function(message){
     processUserMessage(user, message);
     var nextUser = findNextUser(user);
     if (nextUser)
         processChunk(nextUser);
     else
         allFinished();
   }});
};

processChunk(firstUser);
// At this point, none of the requests have returned. They will start arriving later.