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JavaScript JavaScript Array Iteration Methods Array Manipulation Practice reduce()

Posted by Hanwen Zhang
Hanwen Zhang
20,084 Points

Why my code is not working here using includes()? Thanks

phoneNumbers is array of 10 digit phone numbers, where the first three digits, in parentheses, are area codes. Using reduce, return the total phone numbers with a 503 area code. Store the total in the variable numberOf503.

app.js 
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,areaCode)=>{
  if(areaCode.includes('(503)')){
    count+=1
  }
  return count;
},0);

1 Answer

Peter Vann
Peter Vann
36,427 Points

Hi Hanwen!

Your biggest issue is just not doing the last step (storing the value produced by the reduce method).

The giveaway is that numberOf503 has been declared, but you haven't used it.

This passes:

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, phoneNumber) => { // This is what was missing
  if(phoneNumber.includes('(503)')){
    count += 1;
  }
  return count;
},0);

The rest of your code what correct.

I just changed areaCode to phoneNumber, because to me, it's more accurate, semantically.

I hope that helps.

Stay safe and happy coding!

Hanwen Zhang
Hanwen Zhang
20,084 Points

Got it, thank you Peter