Function arrFindLast

The arrFindLast() method iterates the array in reverse order and returns the value of the first element that satisfies the provided testing function. If no elements satisfy the testing function, undefined is returned.

• If you need the index of the found element in the array, use arrFindLastIndex().
• If you need to find the index of a value, use arrLastIndexOf(). (It's similar to arrFindLastIndex(), but checks each element for equality with the value instead of using a testing function.)
• If you need to find if a value exists in an array, use arrIncludes. Again, it checks each element for equality with the value instead of using a testing function.
• If you need to find if any element satisfies the provided testing function, use arrSome.

The arrFindLast() method is an iterative method. It calls a provided callbackFn function once for each element in an array in descending-index order, until callbackFn returns a truthy value. arrFindLast() then returns that element and stops iterating through the array. If callbackFn never returns a truthy value, arrFindLast() returns undefined.

callbackFn is invoked for every index of the array, not just those with assigned values. Empty slots in sparse arrays behave the same as undefined.

arrFindLast() does not mutate the array on which it is called, but the function provided as callbackFn can. Note, however, that the length of the array is saved before the first invocation of callbackFn. Therefore:

• callbackFn will not visit any elements added beyond the array's initial length when the call to arrFindLast() began.
• Changes to already-visited indexes do not cause callbackFn to be invoked on them again.
• If an existing, yet-unvisited element of the array is changed by callbackFn, its value passed to the callbackFn will be the value at the time that element gets visited. Deleted elements are visited as if they were undefined.

const inventory = [
  { name: "apples", quantity: 2 },
  { name: "bananas", quantity: 0 },
  { name: "cherries", quantity: 5 },
];

function isCherries(fruit) {
  return fruit.name === "cherries";
}

console.log(arrFindLast(inventory, isCherries));
// { name: 'cherries', quantity: 5 }

function isPrime(element, index, array) {
  let start = 2;
  while (start <= Math.sqrt(element)) {
    if (element % start++ < 1) {
      return false;
    }
  }
  return element > 1;
}

console.log(arrFindLast([4, 6, 8, 12], isPrime)); // undefined, not found
console.log(arrFindLast([4, 5, 7, 12], isPrime)); // 7

// Array Like
console.log(arrFindLast({ length: 4, 0: 4, 1: 6, 2: 8, 3: 12 }, isPrime)); // undefined, not found
console.log(arrFindLast({ length: 4, 0: 4, 1: 5, 2: 7, 3: 12 }, isPrime)); // 7
Copy