Javascript - Check if 2 items exist in array [duplicate]

Question

In Javascript, how can I ensure that the array of ages has both ages 10 and 18 and not just one.

var ages = [3, 10, 18, 20];
ages.filter(age => age === 10 || age === 18); // returns 10 and 18
ages.filter(age => age === 10 && age === 18); // returns null

The && doesn't ensure that both exist, as it returns null. I know I can use 2 different ages.find/filter and check the combined result, but I am wondering if there is a more elegant way of doing this in a single statement.

To clarify, in the ages array, if I check for 10 (exists) and 21 (doesn't exist), it should return null or false, as one of them does not exist.

new Set(ages.filter(age => age === 10 || age === 18)).size >= 2 — byxor
– byxor, Commented Jan 21, 2017 at 17:23
I think its best to use 2 different filters since in an iteration, age can just be a single number, either 10 or 18 so if you use &&, one of them will always be false. — Ali Baig
– Ali Baig, Commented Jan 21, 2017 at 17:26
@SpencerWieczorek not a duplicate, I am trying to ensure both exist at once, not just one... — Wonka
– Wonka, Commented Jan 21, 2017 at 17:31
Checking for two is just checking for a single one twice. This is a duplicate in the same way finding element a and element b is a duplicate for finding element a. So other than just if ( ages.indexOf( 10 ) > -1 ) it's just if ( ages.indexOf( 10 ) > -1 && ages .indexOf( 18 ) > -1). That's why it's a duplicate. — Spencer Wieczorek
– Spencer Wieczorek, Commented Jan 21, 2017 at 19:13

Community · Accepted Answer · 2020-06-20 09:12:55Z

5

You have to use includes function:

var ages = [3, 10, 18, 20];
console.log(ages.includes(10) && ages.includes(18));

Another method is to use indexOf method:

arr.indexOf(searchElement)

arr.indexOf(searchElement, fromIndex)

var ages = [3, 10, 18, 20];
console.log(ages.indexOf(10)!=-1 && ages.indexOf(18)!=-1);

findIndex is another method that you can use.It actions like indexOf, but there are some differences:

Array.prototype.indexOf() expects a value as parameter. This is usefull for arrays of primitive types,such as Number, String, Boolean.

Array.prototype.findIndex() have a callback function as first parameter. This is usefull specially when you have array of objects.

var ages = [3, 10, 18, 20];
var bool=ages.findIndex(a=>a==10)!=-1 && ages.findIndex(a=>a==18)!=-1;
console.log(bool);

edited Jun 20, 2020 at 9:12

CommunityBot

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answered Jan 21, 2017 at 17:26

Mihai Alexandru-Ionut

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3 Comments

Wonka Over a year ago

works like a charm, thanks for including both ways :)

Thomas Over a year ago

instead of using findIndex() != -1 I'd rather use some(). ages.some(v => v === 10) && ages.some(v => v === 18)

Mihai Alexandru-Ionut Over a year ago

Thanks for your point ! You can include sugestion inside my answer if you wish.Good point.

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