6.1 JavaScript Objects and Object- Oriented Programming (OOP)

2 Motto: My object all sublime I shall achieve in time. —W. S. Gilbert

3 JavaScript & OOP JavaScript is object-oriented –even if you don’t realize it –there is a “global object” all global variables and functions are its properties –there are predefined JS objects –you can add variables and functions to an object's "prototype" (aka classe) –you can – and should define your own objects

4 JavaScript Objects Objects have –a type the type has a name –attributes properties –behaviors functions in JavaScript, functions are properties, too!

5 Object-Oriented design Uses software models that define objects similar the real- world objects in the problem domain Uses classes for objects that have the same characteristics Uses inheritance to derive a new classes of objects from existing classes by adding their own unique characteristics Models communication between objects Encapsulates attributes and behaviors of objects by restricting their visibility to outside objects Allows to redefine the behaviors of derived objects - polymorphism Is a natural and intuitive way to view software design

6 Procedural vs. OOP Procedural programmers concentrate on writing functions –actions that perform a task are composed within functions –a set of functions forms a program Object-oriented programmers concentrate on creating classes of objects –a class contains data and functions that provide services to clients –a set of classes forms a program

7 Advantages of OOP A class is to its objects as cookie-cutter is to cookies OOP make you think in categories OOP make you tackle large problems in terms of smaller sub-problems Classes make it possible to reuse them in other projects With OOP, you can build much of new software by combining existing classes

8 Standard Objects: Math Math defines methods for most common mathematical calculations –the methods are very similar to those in Java java.lang.Math –constants PI, E, LN2, LN10, SQRT2, SQRT1_2 c LOG2E, LOG10E –methods sqrt(), sin(), cos(), tan(), atan(), exp(), log(), pow() ceil(), floor(), round(), max(), min()

9 Standard Objects: String A string is a series of characters –as in Java: letters, digits, special characters Unicode characters same notation – \n, \t, \f, \c, \", \', \\ String constants –can be enclosed either in "" or in '' concatenation operator + –any type concatenated with a string will be converted to a string –using its toString() method property length –holds the number of characters in the string

10 String Methods charAt(index) –returns the character at index –Indices start at 0 and go to length-1 –returns an empty string if index >= length charCodeAt(index) –returns the Unicode value of the character at index –returns NaN if index >= length toLowerCase() –returns the lowercase version of the string toUpperCase() –returns the uppercase version of the string indexOf(pattern[,startIndex]) –returns the beginning index of the first occurrence of pattern –returns -1 if pattern is not found –starts search at startIndex if it is given lastIndexOf(pattern[,startIndex]) –returns the beginning index of the last occurrence of pattern –returns -1 if pattern is not found –starts search at startIndex if it is given

11 String Methods (cont.) split(pattern) –breaks a string into token strings delimited by pattern –returns an array of the tokens substring(from[,to]) –returns the substring starting at from index up to to index –ends the string returned at length-1 if to >= length fixed() –returns this string wrapped into strike() –returns this string wrapped into sub() –returns this string wrapped into sup() –returns this string wrapped into link(url) –returns this string wrapped into anchor(anchor) –returns this string wrapped into