Find Last Index

Requirements

• Implement findLastIndex(array, predicate), examining indices in descending order. Return the matching index, not the value.
• Call predicate(value, index, originalArray). A truthy result is a match; stop immediately when it is found.
• Return -1 for an empty array or when no element matches. Index 0 is a valid result.
• Visit sparse slots too, passing undefined as their value. Preserve original indices and do not mutate the array.
• Do not use Array.prototype.findIndex, findLastIndex, find, or findLast. Assume a valid predicate that does not mutate the array; propagate errors it throws.

Examples

Input: findLastIndex([3, 8, 5, 10], (value) => value > 6)
Output: 3

Input: findLastIndex([1, 2], (value) => value > 9)
Output: -1

Input: findLastIndex([7], (value) => value === 7)
Output: 0