Replacing the nth instance of a regex match in Javascript

Question

I\'m trying to write a regex function that will identify and replace a single instance of a match within a string without affecting the other instances. For example, I have

Answer 1

function pipe_replace(str,n) {
    m = 0;
    return str.replace(/\|\|/g, function (x) {
        //was n++ should have been m++
        m++;
        if (n==m) {
            return "&&";
        } else {
            return x;
        }
    });
}