return list of duplicate elements in an array javascript code example

Example 1: javascript get duplicates in array

function getDuplicateArrayElements(arr){
    var sorted_arr = arr.slice().sort();
    var results = [];
    for (var i = 0; i < sorted_arr.length - 1; i++) {
        if (sorted_arr[i + 1] === sorted_arr[i]) {
            results.push(sorted_arr[i]);
        }
    }
    return results;
}

var colors = ["red","orange","blue","green","red","blue"];
var duplicateColors= getDuplicateArrayElements(colors);//["blue", "red"]

Example 2: check for duplicates in array javascript

[1, 2, 3].every((e, i, a) => a.indexOf(e) === i) // true

[1, 2, 1].every((e, i, a) => a.indexOf(e) === i) // false