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JavaScript JavaScript Array Iteration Methods Array Manipulation Practice reduce()

Posted by Marquis Briggs
Marquis Briggs
8,967 Points

Using reduce, return the total phone numbers with a 503 area code. Store the total in the variable numberOf503.

Not sure what the problem is

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 = phoneNumbersreduce(count, phoneNumber) => 
(phoneNumber.includes('(503)')){
  count +=1; 
}
return count; 
},0);

1 Answer

Juan Luna Ramirez
Juan Luna Ramirez
9,038 Points
Juan Luna Ramirez
Juan Luna Ramirez
9,038 Points 
const phoneNumbers = ["(503) 123-4567", "(646) 123-4567", "(503) 987-6543", "(503) 234-5678", "(212) 123-4567", "(416) 123-4567"];
let numberOf503;

// 1. forgot the period between phoneNumbers and reduce
// 2. take care when passing in a function to another function.
//    You are missing a parentheses for the arguments. Also the
//    curly braces for the body of the reducer function.
numberof503 = phoneNumbers.reduce((count, phoneNumber) => {
  // 4. use if statement
  if (phoneNumber.includes('(503)')){
    count +=1; 
  }

  return count; 
} ,0);

I often mess up the syntax for the reducer function so usually I will do this:

  1. setup an empty reducer function as the first argument and the initial value as the second argument of reduce

    numberOf503 = phoneNumbers.reduce(() => {}, 0)

  2. add the accumulator and item parameters to the reducer function

    numberOf503 = phoneNumbers.reduce((count, phoneNumber) => {}, 0)

  3. break up at the body and begin writing the body of the reducer function

    numberOf503 = phoneNumbers.reduce((count, phoneNumber) => {
// reducer function logic here
}, 0)