JavaScript Objects

Objects in JavaScript

• Objects store multiple pieces of related data in a structured format
• Objects can be thought of as a container that groups different information together
• Objects have attributes (properties) that describe its characteristics
  • Example: A Car object has attributes like color, brand, model, and speed
• Objects also have behaviors (methods) that define actions an object can perform
  • Example: A Car object can have behaviors like start(), stop(), and accelerate()
• A real-life example of an object is a car, which has a brand (e.g., "Dodge"), a color (e.g., "Red"), a speed (e.g., 120 km/h), and can perform actions like starting the engine, accelerating, or stopping
• Another real-life example of an object is a person which has a name (e.g., "Ahmed"), an age (e.g., 25 years old), a job (e.g., "Teacher"), and actions they can perform, like speaking or walking
• JavaScript variables holds a single value
• Objects groups everything together in one place.
• Custom objects are assigned properties as a comma-separated list of name:value pairs within {} curly brackets.

Accessing and extending Objects

• You can reference object property values in two ways: dot or bracket notation
  • Dot Notation: objectName.propertyName
  • Bracket Notation: objectName['propertyName']
• Use dot notation to call methods: objectName.methodName()
• JavaScript objects are dynamic, meaning you can extend or update them easily
• You can add new properties at any time
• You can update an object’s properties simply by assigning a new value
• If a property doesn’t exist, it will be added dynamically
• You can remove properties when needed using the delete keyword.
• Object property values can be referenced using dot notation syntax or by quoting their name between [] square brackets.
• Object methods are called by appending () parentheses after the object’s method name.

Built In Objects

• Most built-in objects (except Math) have a constructor method
• Use new only with Date and Error
• Avoid using new with String, Number, or Boolean since JavaScript recognizes their types automatically
• All built-in objects inherit from Object.prototype

Arrays

• An array is a built-in JavaScript object that stores multiple values in a single variable
• Using an array literal is the easiest way to create a JavaScript Array
• Arrays can store different data types (numbers, strings, objects, etc.)
• In JavaScript Arrays, square brackets [] are used for declaration
• Elements are automatically indexed starting from 0 (zero-based index)
  • For example: let colors = ["Red", "Blue", "Yellow"];
• Arrays can also be created by first declaring and then providing elements.
  • For example:

const cars = [];
cars[0]= "Saab";
cars[1]= "Volvo";
cars[2]= "BMW";

• You can also use the JavaScript Keyword new to create and assign values to Arrays
  • For example: const cars = new Array("Saab", "Volvo", "BMW");
• Using new Array(n) with a single number creates an empty array with n slots, instead of storing the number
  • For example: const cars = new Array(10); creates 10 empty, uninitialized slots.
• JavaScript interprets a single number as the length of the array, not as an element
• The JavaScript built-in Array object stores items in individual elements that are numbered starting at zero.
• Values can be assigned to an array as a comma-separated list within [] square brackets.
• Each Array object has a length property and methods that can be used to manipulate the elements in the array.

Loops

• A loop is a programming construct that allows you to repeat a set of instructions multiple times
• Loops allow you to efficiently fill an array, even for large datasets
  • An example using a for loop to populate an array:

const numbers = [];
for (let i = 0; i < 10; i++) {
  numbers[i] = i * 2;
}
console.log(numbers);

• Looping Through Arrays:

const numbers = [10, 20, 30, 40,50];
for (let i = 0; i < numbers.length; i++) {
  console.log('Index', i, numbers[i]);
}

JavaScript Date object

• The JavaScript Date object represents date, time, and timezone information
• A new Date object is created using the new keyword: const currentDate = new Date();
• By default, it captures the system’s local time without ensuring accuracy to UTC or GMT
• The JavaScript Date object provides separate methods to extract each of its date components for the year, month name, day of the month, and the day name.
• The JavaScript built-in Date object provides separate methods to extract each of its date and time components.

Methods return values

• getFullYear() returns Year as four digits (yyyy)
• getMonth() returns Month as index number (0-11)
• getDate() returns Day as number (1-31)
• getDay() returns Weekday as index number (0-6)
• getHours() returns Hour as number (0-23)
• getMinutes() returns Minute as number (0-59)
• getSeconds() returns Second as number (0-59)
• getMilliseconds() returns Millisecond as number (0-999)