How to identify Loop is completed

Question

I want to minimize following code. Working in node js

var each = 0;
var final = {};
// myLoop have some array values;
myLoop.forEach(function(row) {

    //data retrive from db
    db.query('SELECT * FROM test where type=?',[row.type], function(err, result) {
        final[each] = result;
        each++;
        if (each == myLoop.length) {
           return final;
        }
    });

});

Above code working fine, but trying to avoid if (each == myLoop.length) condition. Is anything available to identify the loop is completed?

Is possible something like below:

myLoop.forEach(function(row) {
    //do needs
}).done({
    return final;
});

UM, if the Ajax code is asynchronous, your logic is flawed in more that one way. — epascarello, Aug 29 '14 at 18:04
@suresh.g - I mean, the classical approach would be to just return final once the loop runs *outside* of the forEach so that it is fully populated. The only reason that wouldn't work is if the db call was async hence my question. — Travis J, Aug 29 '14 at 18:04
@TravisJ Sorry, im confused the word asynchronous, and i updated my question, please have a look — suresh gopal, Aug 29 '14 at 18:14

score 1 · Answer 1 · answered Aug 29 '14 at 21:08

1

Looks like your need should cooperate with DB side.

Even the async.each determines if all callbacks are completed through counting

If you use MongoDB with node driver, you can try to issue your queries in aggregation

answered Aug 29 '14 at 21:08

mevernom

90
6

score 0 · Answer 2 · answered Aug 29 '14 at 17:56

You can do this via Caolan's Async library (or you can take a look how it is done in this lib) - https://github.com/caolan/async#each

// assuming openFiles is an array of file names 

async.each(openFiles, function( file, callback) {

  // Perform operation on file here.
  console.log('Processing file ' + file);

  if( file.length > 32 ) {
    console.log('This file name is too long');
    callback('File name too long');
  } else {
    // Do work to process file here
    console.log('File processed');
    callback();
  }
}, function(err){
    // if any of the file processing produced an error, err would equal that error
    if( err ) {
      // One of the iterations produced an error.
      // All processing will now stop.
      console.log('A file failed to process');
    } else {
      console.log('All files have been processed successfully');
    }
});

score 0 · Answer 3 · answered Aug 29 '14 at 18:01

0

Well in the short term, you could make use of forEach's index:

var final = {};
// myLoop have some array values;
myLoop.forEach( function( row, index ) {
    //data retrive from db
    final[ index ] = row;
    if (index === myLoop.length) {
        return final;
    }
});

And why are you returning 'final'? Were you hoping to do something like trigger an event instead?

answered Aug 29 '14 at 18:01

stakolee

893
1
7
20

Sorry, Actually i did same as you provided. But i mentioned what im expecting – suresh gopal Aug 29 '14 at 18:02
My need is to avoid **if (index === myLoop.length) {** – suresh gopal Aug 29 '14 at 18:04

V31 · Answer 4 · 2014-08-29T18:57:23.133

0

You can make use of the callback function. It will get executed only when everything is completed.

 // Call the function
 loopTheArray(myLoop,function(final){
    //Do whatever you want with final
 });

function loopTheArray(myLoop,callback){
    var final = {},each=0;
    myLoop.forEach(function(row) {
        //data retrive from db
        final[each] = row;
    });
    callback(final);
}

Working Fiddle

edited Aug 29 '14 at 18:57

answered Aug 29 '14 at 18:06

V31

7,626
3
26
44

Here, my problem is the callback(final) function will be execute before the myLoop is fully completed – suresh gopal Aug 29 '14 at 18:09
@suresh.g: This cannot be. added a fiddle to demonstrate how its working. It will work since forEach is blocking. For reference see this link http://stackoverflow.com/questions/5050265/javascript-nodejs-is-array-foreach-asynchronous – V31 Aug 29 '14 at 18:58
Actually im having database query inside loop. so, definitely the callback(final) will be execute before myLoop complete – suresh gopal Aug 29 '14 at 19:24

How to identify Loop is completed

4 Answers4