Simple & Generic Way to Iterate Backwards & Forwards through an Array

arrayIterator.ts

public iterateBackwards (arrayLength: number, index: number): number {
    return index = (index <= 0) ? arrayLength - 1 : --index, index;
}

public iterateForwards (arrayLength: number, index: number): number {
    return index = (index >= arrayLength - 1) ? 0 : ++index, index;
}

/*
 * Usage
 */
const myArray: Array<any> = ['1','2','3','4'];
const length: number = myArray.length;
let index: number = 0;

index = iterateBackwards(length, index); //prints 3
index = iterateBackwards(length, index); //prints 2
index = iterateBackwards(length, index); //prints 1
index = iterateBackwards(length, index); //prints 0

index = iterateForwards(length, index); //prints 1
index = iterateForwards(length, index); //prints 2
index = iterateForwards(length, index); //prints 3
index = iterateForwards(length, index); //prints 0