node.js for loop execution in a synchronous manner

Question

I have to implement a program in node.js which looks like the following code snippet. It has an array though which I have to traverse and match the values with database table entries. I need to wait till the loop ends and send the result back to the calling function:

var arr=[];
arr=[one,two,three,four,five];

for(int j=0;j<arr.length;j++) {

   var str="/^"+arr[j]+"/";

   // consider collection  to be a variable to point to a database table

   collection.find({value:str}).toArray(function getResult(err, result) {
     //do something incase a mathc is found in the database...
   });

}

However, as the str="/^"+arr[j]+"/"; (which is actually a regex to be passed to find function of MongoDB in order to find partial match) executes asynchronously before the find function, I am unable to traverse through the array and get required output.

Also, I am having hard time traversing through array and send the result back to calling function as I do not have any idea when will the loop finish executing.

arb · Accepted Answer · 2014-02-25 14:07:26Z

4

Try using async each. This will let you iterate over an array and execute asynchronous functions. Async is a great library that has solutions and helpers for many common asynchronous patterns and problems.

https://github.com/caolan/async#each

Something like this:

var arr=[];
arr=[one,two,three,four,five];

asych.each(arr, function (item, callback) {
  var str="/^"+item+"/";
  // consider collection  to be a variable to point to a database table
  collection.find({value:str}).toArray(function getResult(err, result) {
    if (err) { return callback(err); }
    // do something incase a mathc is found in the database...
    // whatever logic you want to do on result should go here, then execute callback
    // to indicate that this iteration is complete
    callback(null);
  });
} function (error) {
  // At this point, the each loop is done and you can continue processing here
  // Be sure to check for errors!
})

edited Feb 25, 2014 at 14:07

answered Feb 25, 2014 at 14:01

arb

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arb Over a year ago

@user3256628 if this answer helped you, please consider marking this as the answer to this question.

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