Números duplicados en una matriz JavaScript
[1, 1, 2, 2, 3].filter((element, index, array) => array.indexOf(element) !== index) // [1, 2]
Smarty Hearty
[1, 1, 2, 2, 3].filter((element, index, array) => array.indexOf(element) !== index) // [1, 2]let arr =["a","b","c"];
// ES6 way
const duplicate = [...arr];
// older method
const duplicate = Array.from(arr);