JS Class & Objects

JS Classes

• In JavaScript, classes were introduced in ECMAScript 2015 (ES6) as a new way of defining objects and object-oriented programming.
• A class in JavaScript is a blueprint for creating objects with properties and methods.
• To create a class in JavaScript, the class keyword is used and followed by the class name.
• In JavaScript, classes can be created using the class keyword. The basic syntax for creating a class in JavaScript is as follows:-

JS Object

• • The object is one of the significant and broad data types of JS which represents instances through which we can access member’s data.
  • JavaScript is an object-based scripting language. It allows us to define our own objects and make our own variable types.
  • It also offers a set of predefined objects. The tables, forms, buttons, images, or links on our web page are examples of objects.
  • JS Object’s Property & Methods:
    • JS objects are composed of attributes. When an attribute contains a function, it is considered to be a method of the object, otherwise, the attribute is considered a property.
    • There is a small difference between a function and a method i.e. a function is a standalone unit of statements and a method is attached to an object and can be referenced by this keyword.
    • The values associated with objects are properties and the actions that can perform on objects are methods or behavior.
    • The syntax for adding a property to an object is (i.e. Property associated with an object can be accessed) as follows:-
      objectName.object property name = propertyValue; 
  • To create user-defined objects (not built-in objects) –
    • In JavaScript, objects can be created using the object literal syntax, constructor functions, and the Object.create() method [Explained in program examples topics].

• • Some popular predefined objects in JavaScript are:-
    • DOCUMENT OBJECT:-
      • The Document object is one of the parts of the Window object.
      • It can be accessed through the window—document property.
      • The document object represents a HTML document and it allows one to access all the elements in a HTML document.
      • For example, the title of the current document can be accessed by “document.title” property.
      • Some of the common properties of document objects are :-

Title : returns/ sets the title of the current document.
bgColor : returns/ sets the background color of the recent document.
fgColor : returns/ sets the text color of the recent document.
linkColor : returns/ sets the color of hyperlinks in the document.
alinkColor : returns/ sets the color of active links in the document.
vlinkColor : returns/ sets the color of visited hyperlinks.
height : returns the height of the current document.
width : returns the width of the recent document.
Forms : returns a list of the FORM elements within the current document.
Images : returns a list of the images in the current document.
URL : returns a string containing the URL of the current document.
Location : to load another URL in the current document window

• • • • Some of the common methods of the document object are :-

open() : Opens a document for writing.
write() : Writes string/data to a document.
writeln() : Writes string/data followed by a newline character to a document.
close() : Closes a document stream for writing.

• • • • Examples of properties and methods of the document object are :- 

                                 <script>

</script>

• • • DATE OBJECT :
      • Date object is used to set and manipulate date and time.
      • JavaScript dates are stored as the number of milliseconds since midnight, January 1, 1970. This date is called the epoch. Dates before 1970 are represented by negative numbers.
      • A date object can be created by using the new keyword with Date().
      • Syntax

newDate()
new Date(milliseconds)
new Date(dateString)
new Date(yr_num, mo_num, day_num [,hr_num, min_num, sec_num, ms_num])

• • • • Some common methods of Date Object are –
        • We can use the get methods to get values from a Date object.
        • Here are  some common get methods that return some date-related value according to local time :

getDate( ) : Returns the day of the month
getDay( ) : Returns the day of the week
getFullYear( ) : Returns the full year
getHours( ) : Returns the hour
getMinutes( ) : Returns the minutes
getMonth( ) : Returns the month
getSeconds( ) : Returns the seconds
getTime( ) : Returns the numeric value corresponding to the time
getYear( ) : Returns the year

• • • • Example :

• • • MATH OBJECT : 
      • This object contains methods and constants to carry out more complex mathematical operations.
      • This object cannot be instantiated like other objects.
      • All properties and methods of Math are static.
      • Some common properties of Math objects are – 

Math.PI : Returns the value of pi.
Math.LN2 : Natural logarithm of 2.
Math.LN10 : Natural logarithm of 10, approximately 2.302.
SQRT1_2 : Square root of ½.
SQRT2 : Square root of 2.

• • • • Some common methods of Math objects are – 

pow(x, p) : Returns X^P 
abs(x) : Returns absolute value of x.
exp(x) : Returns e^x
log(x) : Returns the natural logarithm of x.
sqrt(x) : Returns the square root of x.
random() : Returns a random number between 0 and 1.
ceil(x) : Returns the smallest integer greater than or equal to x.
floor(x) : Returns the largest integer less than or equal to x.
min(x, y) : Returns the smaller of x and y.
max(x, y) : Returns the larger of x and y.
round(x) : Rounds x up or down to the nearest integer.
sin(x) : Returns the sin of x, where x is in radians.

• • • • Example :