function alphabetSubsequence(str) {
    if (str.length === 0) {
        return false;
    }
    
    const temp = new Set(str.split(''));
    
    if (temp.size !== str.length) {
        return false;
    }
    
    let currentChar = str.charCodeAt(0);
    
    for (char in str) {
        if (str.charCodeAt(char) < currentChar) {
            return false;
        }
        currentChar = str.charCodeAt(char);
    }
    
    return true;
}



/**
* Test Suite 
*/
describe('alphabetSubsequence()', () => {
    it('returns false when it has duplicate letters', () => {
        // arrange
        const str = 'effg';
        
        // act
        const result = alphabetSubsequence(str);

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

    it('returns false when NOT in ascending a - z order', () => {
        // arrange
        const str = 'cdce';
        
        // act
        const result = alphabetSubsequence(str);

        // log
        console.log("result 2: ", result);
        
        // assert
        expect(result).toBe(false);
    });
    
    it('returns true when no duplicates and is ascending a - z order ', () => {
        // arrange
        const str = 'ace';
        
        // act
        const result = alphabetSubsequence(str);

        // log
        console.log("result 3: ", result);
        
        // assert
        expect(result).toBe(true);
    });
    
    it('empty str returns false', () => {
        // arrange
        const str = '';
        
        // act
        const result = alphabetSubsequence(str);
        
        // assert
        expect(result).toBe(false);
    });
});