JSFiddle - React, Tailwind, and code Playground

JavaScript

var a = ['s', 's1', 'd'];

function dups(el) {
    if (a.indexOf(el) !== -1) {
        for (var i = 1; i < Number.MAX_VALUE; i++) {
            if (a.indexOf(el + i) === -1) {
                a.push(el + i);
                break;
            }
        }
    } else {
        a.push(el);
    }
}


dups('s');
dups('s');
dups('s');
dups('d');
console.log(a);