Below is a snapshot of my code from routes/index.js

exports.index = function(req, res){
    var results=new Array();
    for(var i=0; i<1000;i++){
        //do database query or time intensive task here based on i 
        // add each result to the results array
    }
    res.render('index', { title: 'Home !' , results:results });
};

If I run this code , due to the asynchronous nature of javascript the last line gets executed before the loop gets pletely processed . Hence my webpage doesnt have the results . How do I structure this such a way that the page gets loaded once the queries are pleted ?

Updated

Inside the loop I have database code ( Redis ) like the below -

client.hgetall("game:" +i, function(err, reply) {

           results.push(reply.name);
        });

Below is a snapshot of my code from routes/index.js

exports.index = function(req, res){
    var results=new Array();
    for(var i=0; i<1000;i++){
        //do database query or time intensive task here based on i 
        // add each result to the results array
    }
    res.render('index', { title: 'Home !' , results:results });
};

If I run this code , due to the asynchronous nature of javascript the last line gets executed before the loop gets pletely processed . Hence my webpage doesnt have the results . How do I structure this such a way that the page gets loaded once the queries are pleted ?

Updated

Inside the loop I have database code ( Redis ) like the below -

client.hgetall("game:" +i, function(err, reply) {

           results.push(reply.name);
        });

• javascript
• node.js
• asynchronous
• express

• 1 What exactly is in the loop body? Does it support callbacks? – zerkms Commented Dec 17, 2012 at 2:21
• hi zerkms - I just updated the question to add details about that part as well . Yes it supports callbacks. – geeky_monster Commented Dec 17, 2012 at 2:56

2 Answers 2

Use the async library:

exports.index = function(req, res){
    var results=new Array();
    async.forEach(someArray, function(item, callback){
        // call this callback when any asynchronous processing is done and
        // this iteration of the loop can be considered plete
        callback();
    // function to run after loop has pleted
    }, function(err) {
        if ( !err) res.render('index', { title: 'Home !' , results:results });
    });
};

If one of the tasks inside the loop is asynchronous, you need to pass the asynchronous task a callback that calls callback(). If you don't have an array to use in forEach, just populate one with integers 1-1000.

Edit: Given your latest code, just put the async callback() right after responses.push(reply.name).

exports.index = function(req, res) {
  var events = require("events");
  var e = new events.EventEmitter();
  e.expected = 1000;
  e.finished = 0;
  e.results = [];

  e.on("finishedQuery", (function(err, r) {
    this.finished += 1;
    this.results.push(r && r.name);
    if (this.finished === this.expected) {
       res.render('index', { title: 'Home !' , results:this.results });
    };
  }).bind(e));

  for (var i = 0; i < e.expected; i++) {
    client.hgetall("game:" + i, function(err, reply) {
      e.emit("finishedQuery", err, reply);
    });
  };
};

Of course, the above code doesn't handle [1 or more] errors. You'd need to add logic that only responds (1) on the first error or (2) if no errors occur.