Data Types in JavaScript

Data Types

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• JavaScript is a dynamically typed language, meaning the type of a variable is determined at runtime.

Data Types and their Key Differences

There are two main categories of data types:

1. Primitive data types:
   • Primitive types are copied by value, meaning changes to one variable don’t affect another.
2. Non-primitive (reference) data types:
   • Reference types are copied by reference, meaning changes to one reference affect all references to the same object.

1. Primitive Data Types

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Tip

• Primitive data types hold a single value.

1. Number: Represents both integer and floating-point numbers.

   • Examples: 42, -7.5, 0.001
   • Special values: Infinity, -Infinity, NaN (Not a Number)

2. String: Represents a sequence of characters, enclosed in single ('), double ("), or backticks (```) for template literals.

   • Examples: "hello", 'world', `Hi, ${name}`

3. Boolean: Represents a logical value, either true or false.

   • Used in conditional statements and logic operations.

4. Undefined: A variable that has been declared but not assigned a value.

   • Example: let x; (x is undefined)

5. Null: Represents the intentional absence of any value.

   • Example: let y = null;

6. Symbol: A unique and immutable value, often used as object property keys (introduced in ES6).

   • Example: const sym = Symbol('description');

7. BigInt: Represents large integers with arbitrary precision (introduced in ES2020).

   • Example: 12345678901234567890n (note the n suffix)

2. Non-Primitive (Reference) Data Types

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Note

• Non-primitive data types are more complex and can hold multiple values or properties. They are mutable (can be changed) and are stored as references in memory.

• Object: A collection of key-value pairs.
  • Example: const obj = { name: "Alex", age: 30 };
  • Includes special types like:
    1. Arrays: Ordered lists of values.
       • Example: const arr = [1, 2, 3];
    2. Functions: Reusable blocks of code.
       • Example: function greet() { return "Hello"; }
    3. • Dates, RegExp, etc.
       • Example: const date = new Date(); (Date object)
       • Example: const regex = /abc/; (Regular expression object)
       • Example: const regex = new RegExp('abc'); (Regular expression object)

Checking Data Types

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To check the type of a variable, you can use the typeof operator or the instanceof operator.

Tip

• typeof: Returns a string indicating the type of the unevaluated operand.
  • Example: typeof "hello" returns "string"
• instanceof: Tests whether an object is an instance of a specific constructor or class.
  • Example: [] instanceof Array returns true
  • Example: {} instanceof Object returns true

Examples:

• typeof 42 → "number"
• typeof "hello" → "string"
• typeof true → "boolean"
• typeof undefined → "undefined"
• typeof null → "object" (historical quirk in JavaScript)
• typeof {} → "object"
• typeof [] → "object" (use Array.isArray() to check for arrays)
• typeof function(){} → "function"