Basic Data Structures - Iterate Through All an Array's Items Using For Loops

[rosaforrestiana]

Tell us what’s happening:
I don’t understand this code
if (arr[i].indexOf(elem) == -1)

Your code so far
I already got the answer but still cannot figure out why need to use ==-1

function filteredArray(arr, elem) {
  let newArr = [];
  // Only change code below this line
 for (let i = 0; i < arr.length; i++) {
if (arr[i].indexOf(elem) == -1) {
   newArr.push(arr[i]); 
}
  }
  // Only change code above this line
  return newArr;
}

console.log(filteredArray([[3, 2, 3], [1, 6, 3], [3, 13, 26], [19, 3, 9]], 3));

Your browser information:

User Agent is: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/107.0.0.0 Safari/537.36 OPR/93.0.0.0

Challenge: Basic Data Structures - Iterate Through All an Array’s Items Using For Loops

Link to the challenge:
https://www.freecodecamp.org/learn/javascript-algorithms-and-data-structures/basic-data-structures/iterate-through-all-an-arrays-items-using-for-loops`Preformatted text`

[hbar1st]

Ask yourself (or google): what does indexOf do?

[rosaforrestiana]

ok. I think I found the answer.