Besides primitive types, JavaScript has complex data types, primarily Objects.

Objects: An object is a collection of key-value pairs (properties). Properties can be strings, numbers, booleans, functions, or even other objects.

// Object literal syntax
let person = {
  firstName: "John",
  lastName: "Doe",
  age: 30,
  isStudent: false,
  greet: function() { // A method (function property)
    console.log("Hello, my name is " + this.firstName);
  }
};

console.log(person.firstName); // Accessing property: "John"
person.age = 31; // Modifying property
person.greet(); // Calling a method: "Hello, my name is John"

Arrays: An array is a special type of object used to store an ordered list of values. Array elements can be of any data type.

// Array literal syntax
let colors = ["red", "green", "blue"];
let mixedArray = [10, "apple", true, null];

console.log(colors[0]); // Accessing element by index: "red"
colors[1] = "yellow"; // Modifying element
colors.push("purple"); // Adding element to the end
console.log(colors.length); // Getting the number of elements: 4

// Iterating through an array
for (let i = 0; i < colors.length; i++) {
  console.log(colors[i]);
}

Both objects and arrays are reference types, meaning when you assign them to another variable, you are copying a reference to the original object/array in memory, not the object/array itself.