How to check if a value is in an array in JavaScript

By using the JavaScript Array.prototype function includes we can quickly determine if an array contains a certain element. Here's a simple example:

const animals = ['dog', 'cat', 'cow', 'goose', 'bear'];

const containsGoose = animals.includes('goose');

console.log(containsGoose);

// true

If the value isn't in the array the method will return false like so:

const animals = ['dog', 'cat', 'cow', 'goose', 'bear'];

const containsHorse = animals.includes('horse');

console.log(containsHorse);

// false

But what if you need to check that an object inside the array contains an attribute with a given value? Well that becomes slightly more complex. Let's try it using just includes first:

const animals = [
  { name: 'dog', age: 7 },
  { name: 'cat', age: 2 },
  { name: 'cow', age: 16 },
  { name: 'goose', age: 10 },
  { name: 'bear', age: 19 },
];

const hasAge10 = animals.includes((t) => t.age === 10);

console.log(hasAge10);

// false

No bueno, Sadly we can't compare objects directly so includes won't work here. We're going to need to look for an alternative, luckily there's a very similar method that we can pass a function to some. Let's try it with that:

const animals = [
  { name: 'dog', age: 7 },
  { name: 'cat', age: 2 },
  { name: 'cow', age: 16 },
  { name: 'goose', age: 10 },
  { name: 'bear', age: 19 },
];

const hasAge10 = animals.some((t) => t.age === 10);

console.log(hasAge10);

// true

Et voila, now our code behaves as expected. It's worth noting that includes is not supported by internet explorer and you may have to either use a polyfill or fall back on some.