Check and add an element into an array

Question

How do I add an element in to an array if it is not already in the array?

var fruits = ["Banana", "Orange", "Apple", "Mango"];

I read that push() could be used to add items but I'm not sure how to check if an item is already in the array.

possible duplicate of [Determine whether an array contains a value](http://stackoverflow.com/questions/1181575/determine-whether-an-array-contains-a-value) — iamawebgeek, Jul 08 '15 at 12:48
`indexOf` has known issues in IE8. You are using jQuery so it is safe to use `jQuery.inArray()` — rrk, Jul 08 '15 at 12:56

Chrillewoodz · Accepted Answer · 2015-07-08T13:02:51.533

3

Like this:

var fruits = ["Banana", "Orange", "Apple", "Mango"];

if (fruits.indexOf('coconut') === -1) {
  fruits.push('coconut');
}

This will check if "coconut" is in the array, if it's not then indexOf will return -1, which will cause the if statement to run. Therefore pushing "coconut" into the array.

-1 means "not found".

To check if an item is in an array, just do:

if (fruits.indexOf('coconut')) {
  return false;
}

edited Jul 08 '15 at 13:02

answered Jul 08 '15 at 12:42

Chrillewoodz

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@Bekki it checkes "equal value and equal type". – rrk Jul 08 '15 at 12:49
thanks. how do I check if an element is not in an array? – Bekki Jul 08 '15 at 12:53
@Bekki Updated answer. – Chrillewoodz Jul 08 '15 at 12:55

score 3 · Answer 2 · answered Jul 08 '15 at 12:45

3

You can use jquery .inArray()

var fruits = ["Banana", "Orange", "Apple", "Mango"];

//check if is already in the array
if (jQuery.inArray("Banana", fruits) === -1) {
  fruits.push("Banana");
}

console.log(fruits);//prints out ["Banana", "Orange", "Apple", "Mango"]

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>

answered Jul 08 '15 at 12:45

Alex Char

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thanks. Could you briefly say why `===` instead of `==` and what's `-1` – Bekki Jul 08 '15 at 12:47
2

why use jQuery for such simple task ?? – Mateutek Jul 08 '15 at 12:47
Ye a bit overkill if jQuery isn't already being used. Also not as readable I would say when you don't know the parameters of inArray(). But a good solution nontheless. – Chrillewoodz Jul 08 '15 at 12:49
@Mateutek for being sure it will be cross browser compatible – iamawebgeek Jul 08 '15 at 12:49
@Bekki `===` in js is to compare by the type. Also `.inArray()` method returns `-1` when the given element doesn't represent in the array. – Alex Char Jul 08 '15 at 12:50

hsz · Answer 3 · 2015-07-08T12:44:03.040

1

With indexOf method you can check the position of the given element in the array. If -1 is returned, it's not in the array.

if (fruits.indexOf('New item') === -1) {
  fruits.push('New item')
}

edited Jul 08 '15 at 12:44

answered Jul 08 '15 at 12:42

hsz

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Why `add()` and not `push()` ? – Bekki Jul 08 '15 at 12:43
@Bekki It was a mistake, sorry. – hsz Jul 08 '15 at 12:45

score 0 · Answer 4 · answered Jul 08 '15 at 12:43

indexOf() searches for a particular element in the array and returns -1 if element is not present. Then after checking that you can put the element in array using push()

   if(fruits.indexOf('element to be added') === -1)
             fruits.push('element to be added');

score 0 · Answer 5 · answered Jul 08 '15 at 12:45

First you should check if item to enter exists or not. For that use .indexOf() function.

If not, use .push() to add a new item.

DEMO

$(document).ready(function(){
    var fruits = ["Banana", "Orange", "Apple", "Mango"];
    var item_to_enter="Grapes";
    var item_should_not_enter="Apple";

    if(fruits.indexOf(item_to_enter)<0)
    {
        fruits.push(item_to_enter);
    }
    if(fruits.indexOf(item_should_not_enter)<0)
    {
        fruits.push(item_should_not_enter);
    }
    console.log(fruits);
});

Check and add an element into an array

5 Answers5