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Data Types in JavaScript

#datatypes #javascript

A data type refers to the kind of value a variable holds.

JavaScript is a dynamically typed language, meaning the data type is associated with the value, not the variable itself.

For example, a variable that currently holds a number can later be reassigned to a string or an object.

JavaScript broadly classifies data types into two categories:

Primitive Data Types (7)

Primitives are immutable and stored by value.

  1. Number: Represents numeric values, whether integer or floating-point. Examples: 42, 3.14, NaN.
  2. String: Represents text, enclosed in single quotes ' ', double quotes " ", or backticks ` `.
  3. Boolean: Represents logical truth values — true or false. When coerced to numbers, they become 1 and 0 respectively. Commonly used for conditional checks and control flow.
  4. Undefined: Indicates a declared variable that has not been assigned a value. Conceptually borrowed from Scheme.
  5. Null: Represents the intentional absence of any object value (an “empty” reference). Historically inspired by Java’s null.
  6. BigInt: Used for integers larger than Number.MAX_SAFE_INTEGER (2^53 - 1), declared with an n suffix — e.g., 9007199254740993n.
  7. Symbol: Represents unique and immutable identifiers, often used as object keys — no two symbols are ever equal.

Non-Primitive (Reference) Data Types

Non-primitive types are mutable and stored by reference.

  • Object: A collection of key–value pairs, where keys are strings or symbols.

    Example: { name: "Priyasha", age: 25 }

  • Array: An ordered list of elements. Arrays in JavaScript are dynamic and actually specialized objects.

    Example: [1, 2, 3]

Internally, arrays are objects optimized for indexed access. Their size and element types can change at runtime.

  • Function: A callable object. Functions are first-class citizens — they can be stored in variables, passed as arguments, and returned from other functions.
  • Date, RegExp, Map, Set, etc.: These are specialized object types with their own internal behaviors.

In summary, everything in JavaScript is either a primitive or an object.

Primitive values are simple and immutable, while objects are complex and mutable.

Some sources also include Date , Map , Set , and RegExp under non-primitive types, but they are best understood as specialized objects.

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