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How to Check if an Array Includes a Value in JavaScript?

John Au-Yeung
I'm web developer interested in JavaScript stuff.
Originally published at thewebdev.info ・2 min read

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Checking if an array includes a value is something that we’ve to do often in a JavaScript app.

In this article, we’ll look at how to check if an array includes a given value in JavaScript.

Array.prototype.includes

The includes method is a method that’s included with the array instance.

It takes a value and compares it with === to check if an element is included.

For instance, we can write:

console.log(['apple', 'orange', 'grape'].includes('orange'));
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If it’s included, then it returns true .

Otherwise, it returns false .

Array.prototype.indexOf

We can also use the indexOf method of an array instance to check if it includes a given element.

It also uses === for comparison.

And it returns the index of the first instance of an item if it exists.

Otherwise, it returns -1.

To use it, we write:

console.log(['apple', 'orange', 'grape'].indexOf('orange') >= 0);
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Write Our Own

We can write our own function to search for a value.

For instance, we can write:

function contains(a, obj) {
  let i = a.length;
  while (i--) {
    if (a[i] === obj) {
      return true;
    }
  }
  return false;
}

console.log(contains(['apple', 'orange', 'grape'] , 'orange'));
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We create the contains function that uses a while loop to search for an item.

If a[i] has the same value as obj then we return true .

If we loop through the whole a array and didn’t find anything that matches, then we return false .

Array.prototype.some

The some method is another array instance method that comes with JavaScript arrays.

It lets us pass in a callback to check if any items match the given condition.

For instance, we can write:

const items = [{
  a: '1'
}, {
  a: '2'
}, {
  a: '3'
}]

console.log(items.some(item => item.a === '3'))
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We have an items array that has a bunch of objects.

And we call items.some with a callback to check if any items entry with a property equal to 3 exists.

some returns true if an item that matches the given condition exists and false otherwise.

Conclusion

There’re many ways to find if an array item exists in JavaScript.

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