Array.prototype.findIndex()

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

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