Leetcode 791. Custom Sort String javascript

/**
 * @param {string} S
 * @param {string} T
 * @return {string}
 */
var customSortString = function(S, T) {
    let tList = T.split('');
    tList.sort((a, b) => {
        let indexA = S.indexOf(a);
        let indexB = S.indexOf(b);
        return indexA - indexB;
    });
    return tList.join('');
};