compareTwoStrings return wrong output about string-similarity

[semmel]

I notice that if we pass ababacac and abacabac in compareTwoStrings, it return output 1 which is wrong.

It's not wrong, it's just that Sørensen–Dice is abused here for strict string comparison. The first sentence in Wikipedia makes it clear:

The Sørensen–Dice coefficient is a statistic used to gauge the similarity of two samples.

It's in the nature of "statistics" to be blurry.

More fun examples:

stringSimilarity.compareTwoStrings('abaa', 'baab'); // 1
stringSimilarity.compareTwoStrings('baab', 'aaba'); // 1
stringSimilarity.compareTwoStrings('aaba', "abaa"); // 1