JSFiddle - React, Tailwind, and code Playground

JavaScript

function containsDuplicates(arr) {
    var seen = {};
    var duplicate = false;

    for (var i = 0; i < arr.length; i++) {
        if (seen[arr[i]]) {
            duplicate = true;
            break;
        }
        seen[arr[i]] = true;
    }

    return duplicate;
}

var array1 = [1, 2, 3, 4, 5, 6, 7];
var array2 = [1, 1, 2, 3, 5, 8, 13];

console.log(array1);
console.log("Contains duplicates? " + containsDuplicates(array1));
console.log(array2);
console.log("Contains duplicates? " + containsDuplicates(array2));