How to Check if an Array Includes a Value in JavaScript


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If you've been dabbling in JavaScript, you might have encountered a situation where you need to determine whether an array contains a specific value. It's like playing hide and seek with data - you have a value and need to check if it's hiding somewhere in your array. JavaScript provides a simple and efficient method: the includes() method. Let's dive into how this works!

Understanding the includes() Method

Imagine you're at a fruit stand, looking through a basket to find if there's an apple. In JavaScript, your basket is an array, and the apple is the value you're looking for. The includes() method is like asking the fruit vendor, "Do you have any apples in this basket?" If the answer is yes, the method returns true; if not, it returns false.

Here's the basic syntax:

array.includes(valueToFind, [fromIndex])
  • valueToFind: This is the apple you're looking for, or in technical terms, the value you want to check for in the array.
  • fromIndex (optional): This is where you start looking in your basket. If you don't specify this, it starts from the beginning.

A Real Example

Let's say you have an array of programming languages and you want to check if 'JavaScript' is in the list:

const languages = ['Python', 'Ruby', 'JavaScript', 'C++']; const includesJavaScript = languages.includes('JavaScript'); console.log(includesJavaScript); // Output: true

Here, languages.includes('JavaScript') is like asking, "Is 'JavaScript' one of the languages in my list?" Since it is, the output is true.

What about Starting Midway?

You might want to start checking from a specific point in the array, not always from the beginning. This is where fromIndex comes in handy. Consider you're only interested in the latter half of your language list:

const includesRuby = languages.includes('Ruby', 2); console.log(includesRuby); // Output: false

This code checks if 'Ruby' exists in the array starting from index 2 (remember, arrays are zero-indexed in JavaScript). Since 'Ruby' is at index 1, the method returns false.

Case Sensitivity and Type Checking

Remember, includes() is case-sensitive and type-specific. It won't find ' JavaScript ' if you're looking for 'javascript'. Similarly, you'll get different results if you're checking for a number as a string (like '5') versus a number (like 5).

Browser Compatibility

The includes() method is widely supported in modern browsers. However, if you're writing code for an environment that doesn't support ES6 (where includes() was introduced), you might need to use alternatives like indexOf().


Checking if an array includes a specific value in JavaScript is straightforward with the includes() method. It's a powerful tool in your coding toolkit, helping you quickly determine the presence of a value in an array. Remember its case sensitivity; you're good to go on your JavaScript journey. Happy coding!

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