findIndex3.ts

/**
 * Scan the given array to find the index of the element which satisfies the predicate,
 * which receives the previous, current, and next elements every iteration.
 *
 * The `current` element is the element at the "current" index, so returning true in the predicate
 * will cause `findIndex3` to return the index of the `current` element.
 *
 * `previous` will be undefined on the first iteration, and `current` and `next` will be undefined
 * on the previous iteration.
 *
 * If the predicate is not satisfied, a value of -1 is returned.
 *
 * @example
 *   > findIndex3([1, 2, 3], (previous, current, next) => { console.log(previous, current, next) });
 *   undefined, 1, 2
 *   1, 2, 3
 *   2, 3, undefined
 *   3, undefined, undefined
 *   < -1
 *
 * @example
 *   > findIndex3(
 *       [1, 2, 3],
 *       (previous, current, next) => previous && previous % 2 === 1 && next && next % 2 === 1
 *     );
 *   < 1
 */
export function findIndex3<T>(array: T[], predicate: (previous?: T, current?: T, next?: T) => boolean) {
    for (let i = 0; i <= array.length; i++) {
        if (predicate(array[i - 1], array[i], array[i + 1])) {
            return i;
        }
    }
    return -1;
}