Welcome to the Treehouse Community

The Treehouse Community is a meeting place for developers, designers, and programmers of all backgrounds and skill levels to get support. Collaborate here on code errors or bugs that you need feedback on, or asking for an extra set of eyes on your latest project. Join thousands of Treehouse students and alumni in the community today. (Note: Only Treehouse students can comment or ask questions, but non-students are welcome to browse our conversations.)

Looking to learn something new?

Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and a supportive community. Start your free trial today.

JavaScript JavaScript Array Iteration Methods Array Manipulation Practice reduce()

.reduce

How do I complete this challenge.Thanks

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

numberOf503 = phoneNumbers.reduce( (acc, number)=> {
  if(number === subString(503){
        return number;
     }0
})

1 Answer

Jeff Muday
MOD
Jeff Muday
Treehouse Moderator 26,998 Points

You're pretty close to an answer, lets work on that!

You had a little difficulty with syntax. I'll explain as we go along.

The example tests whether you can do counting of the string '(503)'. And, we are going to test each number. You could have easily used a regex, but I will use a SLICE of the array since you would know this.

This answer is a little verbose, but should illustrate the example.

numberOf503 = phoneNumbers.reduce( (acc, number) => {
  // here's where we look for (503)
  if ( number.slice(0,5) === '(503)' ) {
    return acc + 1; // we found a 503, increment the acc.
  } else {
    return acc; //we did not find a 503, skip incrementing
  }
}, 0); // make sure to use an initial value of acc = 0