Which Is Not a Data Type in JavaScript?


Heather Bennett

JavaScript is a versatile programming language that allows developers to create dynamic and interactive websites. As with any programming language, understanding the different data types is essential for writing efficient and bug-free code. In this article, we will explore the various data types in JavaScript and identify which one is not a valid data type.

Data Types in JavaScript:

JavaScript has six primitive data types:
1. Boolean: Represents either true or false. 2. Number: Represents numeric values. 3. String: Represents textual data enclosed within single quotes (”) or double quotes (“”).

4. Null: Represents the intentional absence of any object value. 5. Undefined: Represents the absence of a defined value. 6. Symbol: Introduced in ECMAScript 6, symbols are unique and immutable values that can be used as property keys.

In addition to these primitive data types, JavaScript also has one complex data type called Object. Objects are collections of key-value pairs and can contain properties and methods.

Now that we have an understanding of the various data types in JavaScript, let’s identify which one is not a valid data type.

The Answer: NaN (Not-a-Number)

NaN stands for “Not-a-Number” and is a value returned when a mathematical operation fails or when you attempt to perform an invalid mathematical operation in JavaScript. Although it represents numeric errors, NaN is not considered a number data type.

To check if a value is NaN, you can use the isNaN() function:

const result = isNaN(‘Hello’); // true

In the above example, ‘Hello’ is not a number, so isNaN() returns true.

Common Data Type Mistakes:

When working with JavaScript data types, it’s important to avoid some common mistakes that can lead to unexpected results. Let’s take a look at a few examples:

1. Using a string instead of a number:

const result = ’10’ + 5;
console.log(result); // “105”

In the above example, the string ’10’ is concatenated with the number 5, resulting in the string ‘105’. To perform arithmetic operations, make sure to convert the string to a number using parseInt() or parseFloat().

2. Forgetting to use parentheses:

const result = 10 * 2 + 3;
console.log(result); // 23

In this case, without using parentheses, JavaScript follows the order of operations (PEMDAS/BODMAS). The multiplication operation is performed first, followed by addition.


JavaScript offers a variety of data types that allow developers to work with different kinds of values. Understanding these data types is crucial for writing clean and efficient code.

In this article, we have explored the six primitive data types in JavaScript: Boolean, Number, String, Null, Undefined, and Symbol. We have also discussed the complex data type Object and its characteristics.

Lastly, we learned about NaN (Not-a-Number), which represents numeric errors but is not considered a valid number data type in JavaScript.

Remember to be mindful of common mistakes when working with JavaScript data types and always double-check your code for any unexpected results.

Keep practicing and exploring different aspects of JavaScript to become a proficient developer!

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