CODEWITHSUNDEEP
javascriptnode.jspromise
terra-firma
terra-firma

Reputation: 65

promises not executing sequentially javascript

I have the piece of code below executing using promises.The problem I have is that the promise is not executing sequentially by waiting for the first block to execute before proceeding to the next block

below is the code:

array[]

new Promise(function(resolve, reject) {
//userarray is some array with user id's
userarray.forEach(function(entry) {

    User.findOne({ user_id: entry}, function(err, user) {
       if (err) throw err;
        console.log(user.name);
        array.push(user.name);      
    });
  });
  resolve("success");
})
.then(function() {  
 console.log(array);
 console.log("done");
});

below is the output

[] //array is still empty

done

tom

dick

harry

when what i want is

tom

dick

harry

["tom", "dick", "harry"]

done

Upvotes: 1

Views: 110

Answers (2)

Lifu Huang
Lifu Huang

Reputation: 12778

It seems like User.findOne will call its callback asynchronously so that your promise is resolved before the callbacks are actually invoked. You can try something like this:

var promises = userarray.map(function(entry) {
  return new Promise(function(resolve, reject) {
    User.findOne({ user_id: entry}, function(err, user) {
      if (err) reject(err);
      console.log(user.name); 
      resolve(user.name);
    });
  });
});

Promise.all(promises).then(function(array) {  
  console.log(array);
  console.log("done");
});

Upvotes: 4

xDreamCoding
xDreamCoding

Reputation: 1694

This solution is not really elegant but should get the job done.

var length = userarray.length;
userarray.forEach(function(entry) {

    User.findOne({ user_id: entry}, function(err, user) {
       if (err) throw err;
        console.log(user.name);
        array.push(user.name);  
        if(!--length) resolve("success");
    });
  });
})

Upvotes: 0

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