Welcome to the Treehouse Community

Want to collaborate on code errors? Have bugs you need feedback on? Looking for an extra set of eyes on your latest project? Get support with fellow developers, designers, and programmers of all backgrounds and skill levels here with the Treehouse Community! While you're at it, check out some resources Treehouse students have shared here.

Looking to learn something new?

Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and join thousands of Treehouse students and alumni in the community today.

Start your free trial

JavaScript JavaScript Array Iteration Methods Array Manipulation Practice reduce()

Posted by William Bailey
William Bailey
4,585 Points

Would anyone like to check the following code and then explain to me why i'm not getting the correct result?

const phoneNumbers = ["(503) 123-4567", "(646) 123-4567", "(503) 987-6543", "(503) 234-5678", "(212) 123-4567", "(416) 123-4567"];
let numberOf503;

// numberOf503 should be: 3
// Write your code below
phoneNumbers.reduce((count, value) => {
  const areaCode = value.substr(0,5);
  if (areaCode === '(503)') {
    numberOf503 = count +=1;
  }
  count
}, 0);

2 Answers

Steven Parker
Steven Parker
229,644 Points
Steven Parker
Steven Parker
229,644 Points

The callback function doesn't return anything.

On the line that just has "count" by itself, did you perhaps intend to write "return count;" instead?

Also, the challenge will be expecting you to assign the result of the "reduce" call to "numberOf503" instead of assigning it inside the callback.

William Bailey
William Bailey
4,585 Points
William Bailey
William Bailey
4,585 Points

Thanks so much! The final version of that code is below it was a face-palm once you said that haha. Thanks again.

const phoneNumbers = ["(503) 123-4567", "(646) 123-4567", "(503) 987-6543", "(503) 234-5678", "(212) 123-4567", "(416) 123-4567"];
let numberOf503;

// numberOf503 should be: 3
// Write your code below
numberOf503 = phoneNumbers.reduce((count, value) => {
  const areaCode = value.substr(0,5);
  if (areaCode === '(503)') {
    return count +=1;
  }
  return count;
}, 0);
William Bailey
William Bailey
4,585 Points

The challenge can be solved making the edits above from the original code thanks to Steven's input. :)!~!