JavaScript Learning Notes: Data Types Summary

JavaScript has two main types of values: Primitive and Reference (Non-Primitive).

Primitive Types

Primitive values are immutable and stored directly in memory. There are 7 primitive types:

• String: Represents a sequence of characters.
  const name = "John";
• Number: Represents both integer and floating-point numbers.
  const score = 100;
const scoreValue = 100.3;
• Boolean: Represents true or false values.
  const isLoggedIn = false;
• null: Represents the intentional absence of any object value.
  const outsideTemp = null;
• undefined: Represents a variable that has been declared but not yet assigned a value.
  let userEmail;
• Symbol: Represents a unique and immutable identifier, often used for object property keys.
  const id = Symbol('123');
const anotherId = Symbol('123');
console.log(id === anotherId); // false

  Symbols are always unique, even if they have the same description.

• BigInt: Represents whole numbers larger than the safe integer limit (Number.MAX_SAFE_INTEGER).
  // const bigNumber = 3456543576654356754n;

Reference Types (Non-Primitive)

Reference types are objects that are stored as a reference in memory. When you work with reference types, you're dealing with a reference to the object, not the actual object itself.

• Array: An ordered collection of values.
  const heros = ["shaktiman", "naagraj", "doga"];
• Object: A collection of key-value pairs.
  let myObj = { name: "hitesh", age: 22 };
• Function: A block of code designed to perform a particular task.
  const myFunction = function() { console.log("Hello world"); };

Type Checking

Use typeof to check the type of a variable.