function arrayMaximalAdjacentDifference(nums) {
    //  write code here.
    return nums.reduce((longest, _, index) => {
            let test = 0
            if (index > 0) test = Math.abs(nums[index] - nums[index - 1])
            return longest < test ? test : longest
    }, 0)
}

/**
* 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);
    });
    
    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 3: ", result);
        
        // assert
        expect(result).toBe(11);
    });
});