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JavaScript JavaScript Array Iteration Methods Array Manipulation Practice reduce()


How do I complete this challenge.Thanks

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;

1 Answer

Jeff Muday
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