How can I check same elements in Array?

Question

I have an array, and I want an output if it contains more than 1 of the same element.

Example:

my_array = [1, 2, 3, 1];

Answer 1

if you want a Boolean output if an element is repeated you can do this:

var arr=[1,1,3,4]
let isDup=false;
arr.map(x=>(arr.indexOf(x)!==arr.lastIndexOf(x))?isDup=true:isDup)
console.log(isDup)

Answer 2

Convert the array to a Set. A Set can only contain unique values. If the Set's size is less than the array's length, there are duplicates:

const hasDuplicates = (arr) => arr.length > new Set(arr).size;

console.log(hasDuplicates([1, 2, 3])); // false
console.log(hasDuplicates([1, 2, 3, 1])); // true