Filtering Arrays in JavaScript using Callback Functions

Question

The question is:

"Add code to the functions func1 and func2 in the places marked "ADD CODE HERE" in order to achieve the desired console logs."

function filterArray(array, callback) {
  const newArray = [];
  for (let i = 0; i < array.length; i += 1) {
    if (callback(array[i])) newArray.push(array[i]);
  }
  return newArray;
}
const arrOfNums = [1, 2, 3, 4, 5];
function func1(num) {
  // ADD CODE HERE

}
function func2(num) {
  // ADD CODE HERE

}

 console.log(filterArray(arrOfNums, func1)); // should log: [2, 4]
 console.log(filterArray(arrOfNums, func2)); // should log: [1, 3, 5]

In func1 I tried:

  if (num % 2 === 0) {
    num = num;
  } else {
    num = null;
  }

In func2 I tried:

  if (num % 2 !== 0) {
    num = num;
  } else {
    num = null;
  }

I am unsure how else to approach this problem. My solution did not work and the console.log calls both returned empty arrays...

Thank you in advance!

Your functions don't return anything but the callback functions for filter have to return a boolean for each value. — user16540390
– user16540390, Commented Oct 15, 2021 at 18:19

Jung Ervin · Accepted Answer · 2021-10-15 18:20:57Z

1

The callback function need to give back a boolean value, if true then the filterArray function addig the element to the array.

if (callback(array[i])) newArray.push(array[i]);

So this line only calling the newArray.push(array[i]) if the callback(array[i]) return value is true.

Solution:

function func1(num) {  
   return (num % 2 === 0);
}

function func2(num) {
   return (num % 2 !== 0);
}

answered Oct 15, 2021 at 18:20

Jung Ervin

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1 Comment

Matthew Schwer Over a year ago

Thanks for helping me to understand that it requires a boolean value!

user16540390 · Accepted Answer · 2021-10-15 18:21:21Z

1

Your functions don't return anything but the callback functions for filter have to return a boolean for each value.

You can use

return num % 2 === 0;

resp.

return num % 2 !== 0;

answered Oct 15, 2021 at 18:21

user16540390

1 Comment

Matthew Schwer Over a year ago

Thanks. That is so simple lol! Thank you for helping me to understand that it requires a Boolean!

navnath · Accepted Answer · 2021-10-15 18:21:30Z

0

You need to return true/ false

function filterArray(array, callback) {
  const newArray = [];
  for (let i = 0; i < array.length; i += 1) {
    if (callback(array[i])) newArray.push(array[i]);
  }
  return newArray;
}
const arrOfNums = [1, 2, 3, 4, 5];
function func1(num) {
  // return num % 2 === 0;
  if (num % 2 === 0) {
   return true;
  } else {
    return false;
  }

}
function func2(num) {
  // return num % 2 !== 0;
  if (num % 2 !== 0) {
    return true;
  } else {
    return false;
  }

}

 console.log(filterArray(arrOfNums, func1)); // should log: [2, 4]
 console.log(filterArray(arrOfNums, func2)); // should log: [1, 3, 5]

answered Oct 15, 2021 at 18:21

navnath

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1 Comment

Matthew Schwer Over a year ago

Thank you for taking the time to help! I appreciate it!

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