What Is the Data Type of Variables of in JavaScript?


Larry Thompson

In JavaScript, variables can hold different types of data. The type of data a variable can store is called its “data type”. Understanding the data types in JavaScript is essential for writing efficient and error-free code.

Primitive Data Types

JavaScript has six primitive data types:

  • String: This data type represents a sequence of characters and is denoted by placing the text inside single or double quotes. For example: let name = 'John';
  • Number: This data type represents numeric values, including integers and floating-point numbers. For example: let age = 25;
  • Boolean: This data type represents a logical value, either true or false.

    For example: let isActive = true;

  • null: This data type represents the intentional absence of any object value. For example: let myVariable = null;
  • undefined: This data type indicates that a variable has been declared but has not been assigned any value yet. For example: let myVar;
  • Symbol: This data type represents unique identifiers and is often used as keys in objects.

Non-Primitive Data Type

In addition to the primitive types, JavaScript also has one non-primitive data type called “Object”. Objects are collections of key-value pairs and can contain properties and methods. Objects are created using curly braces ({}) or the object constructor (new Object()).

Determining the Data Type

To determine the data type of a variable, you can use the typeof operator. The typeof operator returns a string indicating the type of the operand.


let name = 'John';
console.log(typeof name); // Output: string

let age = 25;
console.log(typeof age); // Output: number

let isActive = true;
console.log(typeof isActive); // Output: boolean

let myVariable = null;
console.log(typeof myVariable); // Output: object (This is an interesting quirk in JavaScript)

let myVar;
console.log(typeof myVar); // Output: undefined

Type Coercion

In JavaScript, variables can undergo type coercion, which means they can be automatically converted from one data type to another. This can sometimes lead to unexpected results and bugs in your code. It is important to be aware of how JavaScript handles type coercion.


let x = 10;
let y = '5';

console.log(x + y); // Output: "105" (concatenation, since x is coerced into a string)

let z = 10 - '5';

console.log(z); // Output: 5 (subtraction, since both operands are coerced into numbers)


In JavaScript, variables can hold various data types such as strings, numbers, booleans, null, undefined, symbols, and objects. Understanding these data types and how they behave is crucial for writing robust and bug-free code.

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