JSFiddle - React, Tailwind, and code Playground

HTML

<body>
<pre>
<script>

function grid(size) {
    var out = "";
    for (var i = 0; i < size; i++) {
        for (var j = 0; j < size; j++) {
            out += (i == j || i == (size - j - 1)) ? "X" : " ";
        }
        out += "\n";
    }
    return out;
}

document.write(grid(9));

</script>
</pre>
</body>