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JavaScript JavaScript Array Iteration Methods Array Manipulation Practice reduce()

Posted by Muaaz Matwadia
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Muaaz Matwadia
Full Stack JavaScript Techdegree Graduate 19,327 Points

.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 28,722 Points
Jeff Muday
Jeff Muday
Treehouse Moderator 28,722 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