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# How to check if array includes a value in JavaScript?

Here's a Code Recipe to check if a #JavaScript array contains a value. You can use the new array includes method 😋 For older browsers and IE, you can use indexOf 👍

const array = ['🥗', '🍔', '🍰'];

// Modern Browser
array.includes('🍰'); // true

// Older Browser
array.indexOf('🍰') !== -1; // true

# includes with other primitive types

Besides strings, includes also works great with other primitive types.

const symbol = Symbol('symbol');

const array = [
  'string',
  200,
  0,
  undefined,
  null,
  symbol
];

Using includes

array.includes('string'); // true
array.includes(200); // true
array.includes(0); // true
array.includes(undefined); // true
array.includes(null); // true
array.includes(symbol); // true

Using indexOf

array.indexOf('string') !== -1; // true
array.indexOf(200) !== -1; // true
array.indexOf(0) !== -1; // true
array.indexOf(undefined) !== -1; // true
array.indexOf(null) !== -1; // true
array.indexOf(symbol) !== -1; // true

# Caveats of indexOf

So far, I have shown you values where both includes and indexOf work interchangeably. However, there is one value, where they differ 🤭

const array = [NaN];

// ✅
array.includes(NaN); // true

// 😱
array.indexOf(NaN) !== -1; // false

# Checking for Array of Objects using some()

For a more versatile solution that works on other data types, you may want to use some instead.

".some()": tests whether at least one element in the array passes the test implemented by the provided function. It returns a Boolean value.

const array = ['🥗', '🍔', '🍰'];

array.some(food => food === '🍰'); // true

This method is ideal for an array of objects.

const array = [{ name: 'js' }, { name: 'css' }];

array.some(code => code.name === 'js'); // true
array.some(code => code.name === '🤖'); // false

In a previous code note, I talked about a quick & dirty way to check objects using JSON.stringify().

How to Compare 2 Objects in JavaScript

Taking that concept, we can also use it to compare object element in an array like this:

const array = [{ name: 'js' }, { name: 'css' }];

array.some(code => JSON.stringify(code) === JSON.stringify({ name: 'css' }));
// true

# Case Sensitive

Both includes and indexOf are case sensitive:

const array = ['SAMANTHA'];

array.includes('samantha'); // false
array.indexOf('samantha') !== -1; // false

To make it case insensitive, you could consider changing the case of the array like so:

const array = ['SAMANTHA'];

const sameCaseArray = array.map(value => value.toLowerCase());
// ['samantha']

sameCaseArray.includes('samantha'); // true
sameCaseArray.indexOf('samantha') !== -1; // true

But if you were using some, you can do it in one line:

const array = ['SAMANTHA'];

array.some(value => value.toLowerCase() === 'samantha'); // true

# Browser Support

Support for includes is really good for all modern browsers. However, if you need IE or older browser, you will need to use indexOf.

Can I use? Array.prototype.includes

# Community Input

  • @lolinoid: contains > @prvnbist That's a method DOM Nodes, most known example for it would be getting a list of classnames which will be a node list then you can use contain method to see if it has a classname. Or you can convert it to an array and then use includes method

  • You can use the in operator to loop over an object to check if a specific property key exists. (Knowledge shared by @fvbix)

const object = { kiwi: '🥝', pear: '🍐', cheese: '🧀' },;

'kiwi' in object; // true

// Use it as a conditional
if ('kiwi' in object) {
  // do something if property key exists
}
if (~array.indexOf('🍰')) {
  // do something
}
  • @danvc: ~[].indexOf(value). The bitwise ~ operator will return a truthy value for anything but -1. Negating it is as simple as doing !~.

  • @smokku: Bitwise not gives you the opposite of the number, but we use two's complement system to avoid having a +0 and -0. So the negative numbers are shifted by one - where -1 takes place of -0. When we negate the -1 we get +0, which is the only falsey value. All other indices we can get of indexOf() will give you a truthy (non-zero) value when passed through bitwise not ~.

  • @smokku: If you are interested in diving this deep, I highly recommend a book by Charles Petzold called "Code: The Hidden Language of Computer Hardware and Software". It is a fun read, that will guide you from the basics of code design (like Morse, Braile, etc.) through electrical switches and flashing lightbulbs, telegraph, electronic gates and flip-flops, up to the simple CPU level.

# Resources


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