@writetome51/get-index-for-reversed-array/index.js

Function receives array index and returns the new index that same item would have if the array's order were reversed

import {errorIfIndexNotValid} from 'error-if-index-not-valid';
import {errorIfNotIntegerZeroOrGreater} from 'error-if-not-integer-zero-or-greater';


// Receives array `index` and returns the new index that same item would have
// if the array's order were reversed.  Example:  index of 1, for array 6 items long,
// would become index of 4.

export function getIndexForReversedArray(index, arrayLength) {
	errorIfNotIntegerZeroOrGreater(index);
	errorIfIndexNotValid(index, arrayLength);
	return (arrayLength - 1 - index);
}