check if element is repeated in array javascript code example

Example 1: count duplicates array js

uniqueCount = ["a","b","c","d","d","e","a","b","c","f","g","h","h","h","e","a"];
var count = {};
uniqueCount.forEach(function(i) { count[i] = (count[i]||0) + 1;});
console.log(count);

Example 2: javascript check if array has duplicates

function hasDuplicates(array) {
    return (new Set(array)).size !== array.length;
}

Example 3: 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 4: how to count duplicates in an array javascript

arr.reduce((b,c)=>((b[b.findIndex(d=>d.el===c)]||b[b.push({el:c,count:0})-1]).count++,b),[]);

Example 5: js check if array of objects contains duplicates

const arrayOfObjCopy = [...arrayOfObj];

Object.keys(arrayOfObjCopy).forEach((key) => {
  arrayOfObjCopy[key] = JSON.stringify(arrayOfObjCopy[key]);
 });

const arrayOfObjhasDuplicates = uniq(arrayOfObjCopy).length != arrayOfObjCopy.length;

Example 6: check for duplicates in array javascript

[1, 2, 2, 4, 3, 4].filter((e, i, a) => a.indexOf(e) !== i) // [2, 4]