Does it mutate 😱

Array.prototype.findIndex()

No mutation

Description

The findIndex() method returns an index of the first element in the array that satisfies the provided testing function. Otherwise -1 is returned.

arr.findIndex(callback[, thisArg])

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/findIndex

Example

var array1 = [5, 12, 8, 130, 44];

function isLargeNumber(element) {
  return element > 13;
}

console.log(array1.findIndex(isLargeNumber));
// expected output: 3