JSFiddle - React, Tailwind, and code Playground

JavaScript

var Str2 = function (strs, str) {
    var i, a = 0;
    for (i = 0; i < strs.length; i++) {
        if (str == strs[i]) {
            a = a + 1;
            if (a > 1) return "true";
        }
    }
    return "false";
}

var teste1 = Str2(["a", "b", "a", "c"], "c"); //=> "false"
var teste2 = Str2(["a", "b", "a", "c"], "a"); //=> "true"

console.log(teste1, teste2);