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JavaScript JavaScript Array Iteration Methods Array Manipulation Practice reduce()

Posted by Humoyunmirzo Nosirov
Humoyunmirzo Nosirov
Courses Plus Student 5,154 Points

Can anyone find my errors because I can't do that

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 = numberOf503.reduce((count, number) => {
if(number[0] === '503'){
return count;
}
}, 0);

// numberOf503 should be: 3
// Write your code below

2 Answers

Adam Beer
Adam Beer
11,314 Points
Adam Beer
Adam Beer
11,314 Points

number[0] will search for the first character only. I used .slice() method, but you can use .startsWith() method or .substring() method. There are many ways :) Hope this help!

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


numberOf503 = phoneNumbers.reduce((total, phoneNumberString) => {
    if (phoneNumberString.slice(1, 4) === "503") {
    total++;
  }
  return total;
}, 0);
Humoyunmirzo Nosirov
PLUS
Humoyunmirzo Nosirov
Courses Plus Student 5,154 Points
Humoyunmirzo Nosirov
Humoyunmirzo Nosirov
Courses Plus Student 5,154 Points

what does 1 and 4 mean here in if (phoneNumberString.slice(1, 4)

Adam Beer
Adam Beer
11,314 Points
Adam Beer
Adam Beer
11,314 Points

You choose, what's inside the two numbers, so now this equal to '503'. Zero character is the "(". Fourth character is the ")". Inside the two characters you find the "503". When you write the last number, always add one. Hope this help.

String.prototype.slice()