A function which takes an array(ary) and an array of indexes(< ary.length) and sets 'X' for the for ary[indexes] else sets 'O'

tic-tac-toe.js

// in js using for-loop
function swap(ary, indexes) {
    var visited = [];
    var newAry = Array(ary.length).fill(null);
    for(let i=0; i<indexes.length; i++) {
        newAry[indexes[i]] = 'X';
        visited.push(indexes[i]);
    }
    for(let i=0; i<newAry.length; i++) {
        if(newAry[i] === null) {
            newAry[i] = 'O';
        }
    }
    return newAry;
}

// in js using map and filter
let swapp = (ary, indexes) => {
    let newAry = ary.map((aryX, aryI) => {
        let filVal = indexes.filter((indexesX) => {
            return indexesX === aryI ? true : false;
        });
        return filVal[0] === undefined ? 'O' : 'X';
    });
    return newAry;
}

// using python list comprehensions
['X' if index in indexes else 'O' for index, element in enumerate(ary)]