Get the longest subsequence between two strings

gistfile1.txt

function getSubsequences(str){
    let len = str.length, output, counter = 0, result = [];
    for (let i = 1; i < Math.pow(2, len); i++) {
        output = '';
        for (var j = 0; j < len; j++) {
            if (i & (1 << j)) {
                output += str[j];
            }
        }
        counter++;
        result.push(output);
    }
    return result;
}

function getSubstrings(str){
    let i, j, result = [];
    for (i = 0; i < str.length; i++){
        for (j = i+1; j < str.length + 1; j++){
            result.push(str.slice(i, j));
        }
    }
    return result;
}

function sortArrBylength(arr = []){
    const result = arr.sort((a,b) => {
        return b.length - a.length;
    });
    return result;
}

function longestSubsequence(x, y) {
    // Write your code here
    const subsequences = sortArrBylength(getSubsequences(x));
    const substrings = getSubstrings(y);

    let i, result;
    for (i = 0; i < subsequences.length; i++){
        if(substrings.includes(subsequences[i])){
            result = subsequences[i];
            break;
        }
    }

    return result.length;
}

longestSubsequence('abcd', 'abdc');