How to check if JavaScript array contains a value?

This tutorial shows you how to check if a JavaScript array includes a value or not.

1. JavaScript Array.includes()

In JavaScript, there is a built-in array method called includes(), that checks an array contains a certain value or not.

This method returns true If the given value is present in the array, else it will return false.

const fruits = ["Apple", "Banana", "Watermelon", "Pear", "Orange"]

const result = fruits.includes("Banana");
const result2 = fruits.includes("Grapes");

console.log(result)
console.log(result2)

true
false

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2. JavaScript Array.indexOf()

You can use the Array.indexOf() instead of includes(). This method returns the first index number of the given item. But, if the given value does not present in the array, it will return -1.

const fruits = ["Apple", "Banana", "Watermelon", "Pear", "Orange"]

const result = fruits.indexOf("Banana") !== -1;
const result2 = fruits.indexOf("Grapes") !== -1;

console.log(result)
console.log(result2)

true
false

This indexOf() method is not for checking if a value exists in an array or not. Always use the includes() method.

const fruits = ["Apple", "Banana", NaN]

const result = fruits.includes(NaN);
const result2 = fruits.indexOf(NaN) !== -1;

console.log(result)
console.log(result2)//❌ Not work

true
false

How to get the index number of the NaN value?

After seeing the above example, you may be wondering how to get the index number of a NaN value.

So in JS, there is a method called Array.findIndex(), you can use it to get the index number of the NaN value.

const fruits = ["Apple", "Banana", NaN]

const result = fruits.findIndex(Number.isNaN);

console.log(result)

2

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3. Array.some() method

The Array.some() method is almost similar to the findIndex() method, but it returns a boolean value instead of the index number.

It will return true If the given element is found in the array, else it will return false.

const fruits = ["Apple", "Banana", "Watermelon", "Pear", "Orange", "Orange"]

const result = fruits.some(x => x === "Pear");
const result2 = fruits.some(x => x === "Mango");

console.log(result)
console.log(result2)

true
false

Apply the case insensitivity

const fruits = ["Apple", "Banana", "Watermelon", "Pear", "Orange", "Orange"]

const result = fruits.some(x => x === "pear");
const result2 = fruits.some(x => x.toLowerCase() === "pear"); // ✔️ Case insensitivity

console.log(result)
console.log(result2)

false
true