const arrayMaximalAdjacentDifference = nums => 
    nums.reduce((acc, cur, i, a) => 
        i <= a.length - 1 && Math.abs(a[i] - a[i+1]) > acc ? Math.abs(a[i] - a[i+1]) : acc
        , -1
    );

/**
* Test Suite 
*/
describe('arrayMaximalAdjacentDifference()', () => {
    it('returns largest difference between adjacent values', () => {
        // arrange
        const nums = [2, 4, 1, 0];
        
        // act
        const result = arrayMaximalAdjacentDifference(nums);

        // log
        console.log("result 1: ", result);
        
        // assert
        expect(result).toBe(3);
    });

    it('returns largest difference between adjacent values example 2', () => {
        // arrange
        const nums = [2, 9, 1, 0];
        
        // act
        const result = arrayMaximalAdjacentDifference(nums);

        // log
        console.log("result 2: ", result);
        
        // assert
        expect(result).toBe(8);
    });
});