Array.prototype.findLastIndex()

The findLastIndex() method of Array instances iterates the array in reverse order and returns the index of the first element that satisfies the provided testing function. If no elements satisfy the testing function, -1 is returned.

The findLastIndex() 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. findLastIndex() then returns the index of that element and stops iterating through the array. If callbackFn never returns a truthy value, findLastIndex() returns -1.

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.

Syntax example: findLastIndex(callbackFn)