How to find a duplicate in an array of objects in JavaScript?

Question

What am I trying to achieve?

So I have an array which needs to be checked for duplicates and if a duplicate is found I want to display the duplicate found using console.log for now. I must add this this code is based within a function.

The user will then add to this array using some input within the frontend , which is I currently have completed but it is not needed to solve this problem.

Here is my Array below which i want to find if there are duplicates within it.

  const repeatedNumEvent = {
      PlayerNumber: this.state.PlayerNumber,
      eventType: this.state.eventType
    };

basically if an new array object has identical values then display the duplicate

I assume I will have to use a for loop using the .length function but i am unsure how to achieve my task.

Possible array data below

{PlayerNumber: "12", eventType: "Goal"}

If you have any question just ask below. Thanks.

@Chev I have updated my description for you . this is an example which i have got from using console.log() — John, Nov 15 '19 at 02:55
Please, show us a bit of code. I don't see any array, but a simple object with two properties. — Jorge Fuentes González, Nov 15 '19 at 03:10
Are you wanting to find duplicates values within an existing array? Or just check that the value you are trying to add to the existing array is not a duplicate? — Devon Norris, Nov 15 '19 at 03:43

score 2 · Accepted Answer · answered Nov 15 '19 at 03:42

Below should do the trick. It will loop the array and check if we already have the item already. It will console.log as requested, but also leave you with an array of distinct and duplicate items to process as needed

Demo:

const data = [
    {PlayerNumber: "13", eventType: "Goal"},
    {PlayerNumber: "13", eventType: "Goal"},
    {PlayerNumber: "12", eventType: "Goal"},
    {PlayerNumber: "12", eventType: "Goal"},
    {PlayerNumber: "14", eventType: "Goal"}
];

let distinct = [];
let duplicates = [];
data.forEach((item, index, object) => {
    if (distinct.find(current => current.PlayerNumber === item.PlayerNumber && current.eventType === item.eventType)) {
        console.info('duplicate found');

        duplicates.push(item);
    } else {
        distinct.push(item);
    }
});

console.info('duplicates:', duplicates);
console.info('distinct:', distinct);

For sure, wanted to keep it vanilla this time, but highly recommend [lodash](https://lodash.com/) — Samuel Goldenbaum, Nov 15 '19 at 03:47

How to find a duplicate in an array of objects in JavaScript?

1 Answers1