strange bug when adding numbers with nodeJS

Question

So this is most likely simple but I have spent all day trying different approaches and googling for solutions.

for some reason when I use + with 2 numbers instead of adding the numbers together node is joining the numbers.

  Company.findById(req.id, (err, doc) => {

      if (err) {
          callback(err, err);
      } else {

          var i = doc.TotalGranted; // i.e number value of 200
          var e = doc.TotalAvailable; // i.e number value of 200

          var newTotalgranted = i + req.newNumber; // i.e number value of 100
          var newAvailable = e - req.newNumber; // i.e number value of 100

          doc.TotalGranted= newTotalgranted;
          doc.TotalAvailable= newAvailable;

          doc.save((err, doc) => {
              if (err) {
                  callback(err, err);
              }
              callback(null, 'success');
          });
      }
  });

now instead of totalgranted = 300 instead it equals 200,100

if it helps here is the relevant section of the returned document from mongo, these are not contained in an array

  TotalAvailable: 200,
  TotalGranted: 200,



newNumber: '100',

the new number is a string but its actually coming from a returned document as well. so maybe i need to convert the newNumber from a string i have tried this but can not work it out.

"when I use + with 2 numbers" but you don't. A string is not a number! newNumber: '100'. And someString + whatever or whatever + someString performs a string concatenation. That's the expected behaviour, not a bug. — Thomas
– Thomas, Commented Feb 8, 2018 at 7:20

NnN · Accepted Answer · 2018-02-08 07:34:52Z

1

Try,

Company.findById(req.id, (err, doc) => {

  if (err) {
      callback(err, err);
  } else {

      var i = doc.TotalGranted; // i.e number value of 200
      var e = doc.TotalAvailable; // i.e number value of 200

      var newTotalgranted = (i + (req.newNumber * 1)); // i.e number value of 100
      var newAvailable = (e - (req.newNumber * 1); // i.e number value of 100

      doc.TotalGranted= newTotalgranted;
      doc.TotalAvailable= newAvailable;

      doc.save((err, doc) => {
          if (err) {
              callback(err, err);
          }
          callback(null, 'success');
      });
  }
});

edited Feb 8, 2018 at 7:34

answered Feb 8, 2018 at 7:24

NnN

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2 Comments

Thomas Over a year ago

I think the problem in his code is neither i nor e but rather req.newNumber. See newNumber: '100'

NnN Over a year ago

yes, since it is being considered as string we can do a simple multiply of 1 to that will solve this. I made it for i and e which holds number already! Now changed.

Ridham Tarpara · Accepted Answer · 2018-02-08 07:36:09Z

Yeah, you are right, your req.newNumber is a string so javascript by default performs string concatenation. Company.findById(req.id, (err, doc) => {

  if (err) {
      callback(err, err);
  } else {

      var i = doc.TotalGranted; // i.e number value of 200
      var e = doc.TotalAvailable; // i.e number value of 200
      var newNumber = parseInt(req.newNumber);  // or use Number(req.newNumber) or (req.newNumber * 1)
      var newTotalgranted = i + newNumber; // i.e number value of 100
      var newAvailable = e - newNumber; // i.e number value of 100

      doc.TotalGranted= newTotalgranted;
      doc.TotalAvailable= newAvailable;

      doc.save((err, doc) => {
          if (err) {
              callback(err, err);
          }
          callback(null, 'success');
      });
  }
});

this would work but best way will be to take a number from request parameter itself which will reduce your overhead of converting a string into an integer

You can read more about various strategy on number conversion from string here

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