JavaScript Objects

Objects in JavaScript

• Objects store multiple pieces of related data in a structured format, acting as containers that group information.
• An object stores attributes, to describe characteristics of an object
• An object also defines behaviors (methods), which are actions an object can perform.
• Consider "Car" objects, that has attributes like color, brand, model, and speed
• Consider "Car" objects, that have behaviors like start(), stop(), and accelerate().
• A "Person" has a name, age, and job as attributes, and can perform actions like speaking or walking.
• A car has a brand (e.g., "Dodge"), a color (e.g., "Red"), and a speed (e.g., 120 km/h).
• A car can start the engine (start()), accelerate (accelerate()), and stop (stop()).

Representing Objects in JavaScript

• Objects can be represented in JavaScript using the object construct with properties like name, age, and job, along with functions for actions or speaking
• Variables hold a single value while objects group related data together.
• All related information about John is inside one structured unit instead of several independent variables

Accessing Object Properties and Methods

• Object property values can be referenced in two ways: Dot Notation and Bracket Notation.
• Dot Notation example: objectName.propertyName
• Bracket Notation example: objectName['propertyName']
• Dot notation example: objectName.methodName()
• Use dot notation to call methods.

Extending Objects

• Objects in JavaScript are dynamic and can be extended and updated easily
• New properties can be added, existing ones can be modified, and properties can be removed as needed.
• Object properties updated by assigning a new value.
• New properties are added dynamically if they do not already exist.
• To remove properties, the delete keyword can be used
• Example: delete car.color

Built-in Objects

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

JavaScript Arrays

• Arrays are built-in JavaScript objects that store multiple values in a single variable.
• Array Literal is the easiest way to create them
• Arrays can store different data types
• Arrays use square brackets for declaration []
• Elements are automatically indexed starting from 0 (zero-based index).
• Provide the elements when declaring an array.
• The JavaScript keyword new can create arrays and assign values.
• A single numeric argument with new Array(n) creates an empty array that sets the length/number of slots, not the value of the first element.
• Loops are programming constructs that repeat a set of instructions multiple times.
• Use loops to efficiently fill an array, even for large datasets.
• JavaScript array objects can be iterated using for loops, with the array's length property of javascript arrays to specify the number of loop iterations.
• Assigns values to an array as a comma-separated list within square brackets [].

JavaScript Date object

• The JavaScript Date object represents date, time, and timezone information.
• Use the new keyword to create a Date object.
• Date objects capture the system's local time without ensuring accuracy to UTC or GMT.
• Date objects provide separate methods to extract its date and time components
• Date objects include methods to get the year, month, day of the month, and day name
• Date objects provide methods to extract time components like hour, minute, second, and millisecond.
• Date object extract calendar for year as four digits (yyyy) using getFullYear() method
• Date object extract calendar for month as index number (0-11) using getMonth() method
• Date object extract calendar for day as number (1-31) using getDate() method
• Date object extract calendar for weekday as index number (0-6) using getDay() method
• Date object provides separate methods to extract each of its time components for the hour, the minute, the second, and the millisecond.
• Custom objects are assigned properties as a comma-separated list of name:value pairs within { } curly brackets.
• 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.
• 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.
• The JavaScript built-in Date object provides separate methods to extract each of its date and time components.