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Javascript as a Prototype-based Language JavaScript is a prototype-based programming language. In order to help us understand what this means, we can compare JavaScript with different kind of a language. Let’s take a look at languages such as Java and C++. These two are often referred to as Object-oriented languages. One of the fundamental ideas behind these languages is the concept of a class which is like a blueprint for creating an object. What is a class? Let’s start simple. In JavaScript we have the keyword var which is used to define a variable. We can later use this variable in our program to add numbers or concatenate strings. But what does a class define? By itself the keyword class defines a type of something. Literally, it can be a type of anything. This is only limited by your imagination and the purpose of your program. A class is an abstract concept, like a paintbrush. You choose the colors to paint your program with. The keyword class does not exist in JavaScript. But we need to talk about this keyword, and the concept of classes as a computer science subject, only to compare it with JavaScript in order to get a better insight on its prototype-based nature. But there is still a link between classes and JavaScript. That link is the concept of an object. The two languages C++ and Java use objects. So does JavaScript. And in a way a class is an object. And we will see how in just a moment. You may already understand what classes and objects are. But in order to gain a deeper understanding of JavaScript as a prototype-based language we need to briefly discuss them in the following section. Classes and Objects A class can be thought of as a creative logic tool that defines one of the many elements of your computer program. A class is a type of something. It is a blueprint that defines the construction and function a specific object that will be built from that class. Multiple classes can and often are designed to work with each other. That’s the point. You can create a class and call it class car. You can then create a class engine and use it to define an engine for the car. You can create different types of cars by adding different kinds of engines to them. In computer science this is referred to as object composition. Object composition is a method rarely used in JavaScript programs because the prototype method, which we will discuss in a moment, replaces it. 43
An object is created from a class. And in JavaScript everything is an object by definition. This is why we never need to use the class keyword in the first place. Everything is already an object. Whereas in PHP, C++ or Java, this is not true. Conceptually, variables are data types and not necessarily classes in these languages. There is a clear distinction between variables and classes in those languages. But not in JavaScript which treats every single data type as an object by default. This is very important concept to understand and it is part of what makes JavaScript a prototype-based language. In an object-oriented language the entire program is a collection of these objects working together. An object is an initialized class. It is the physical representation of the class in computer memory, that is ready to be used by your program. While the class is merely a blueprint model, a design - the object of that class is the constructed result. The behavior and properties of an object can be defined during the process of object creation, also known as instantiation of an object. In other words, a new instance of an object is created, or initialized, from a specific model which is determined by its class. An object can also be modified by your program during the course of its existence until it is destroyed or in other words, erased from computer memory. Classes are the models for spawning new instances of objects. Using one class, you can spawn any number of different types of cars with different types of engines, transmission systems or tires. The number of objects that can be created is only limited by memory capacity of the computer on which your program is running. An Example of Object Composition. Object-oriented programming languages follow the same idea as in the real world, where real-life objects are constructed from a number of smaller objects. A car has an engine and wheels. A light bulb has a glass shape and socket base type. 44
Page 1 and 2: “ Second Revision. July 2012 Unde
Page 3 and 4: Prototype, JavaScript Objects and J
Page 5 and 6: Thought transcends matter. When we
Page 7 and 8: Preface The purpose of this book is
Page 9 and 10: A Lesson in Creativity The web deve
Page 11 and 12: I love jQuery because it allows me
Page 13 and 14: Improving Page Load Performance The
Page 15 and 16: Determining the Placement of Intern
Page 17 and 18: JavaScript 1. The only language peo
Page 19 and 20: What is JavaScript? Web designers u
Page 21 and 22: As you can see, variables can be as
Page 23 and 24: The example above will first execut
Page 25 and 26: Only variables and events should be
Page 27 and 28: Notice that variables a and b are c
Page 29 and 30: What Exactly is a JavaScript Variab
Page 31 and 32: A variable allocates enough data st
Page 33 and 34: Do you want to really understand pr
Page 35 and 36: What is a Variable? Variables can b
Page 37 and 38: In order to understand bitwise logi
Page 39 and 40: At first this might seem confusing.
Page 41 and 42: Let’s display the variable “a
Page 43 and 44: What’s important is the return va
Page 45 and 46: Inserting Form Values into MySQL Da
Page 47: I like code that you can “read”
Page 51 and 52: Dynamic Prototype-based Objects in
Page 53 and 54: Without knowing anything at all abo
Page 55 and 56: More About JSON JSON is a data inte
Page 57 and 58: In some programming languages the t
Page 59 and 60: JavaScript from scratch. If you are
Page 61 and 62: property access operator - the . (d
Page 63 and 64: Why does jQuery do exactly the same
Page 65 and 66: Learning jQuery The greatest thing
Page 67 and 68: If this sounds like you, then you w
Page 69 and 70: Web App Initialization To initializ
Page 71 and 72: In JavaScript, we can define variab
Page 73 and 74: As mentioned above, to an experienc
Page 75 and 76: Including jQuery In Your Source Cod
Page 77 and 78: Including jQuery as an External CDN
Page 79 and 80: Including jQuery UI In the Starting
Page 81 and 82: What Kind of Elements Can You Selec
Page 83: To traverse the DOM and make sure t
Page 86 and 87: Here is a basic inline CSS example
Page 88 and 89: Because the DIV element has ID of
Page 90 and 91: After selecting all of these input
Page 92 and 93: Figure 1 Mentality of a beginner jQ
Page 94 and 95: Whose Children Are These? If we are
Page 96 and 97: Next, let’s explore the possibili
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jQuery Events Because jQuery is so
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Of course, the effects of binding a
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Using toggle() Events Toggling betw
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Speed Up Your jQuery Code jQuery is
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Let’s now look at the jQuery way
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Practical jQuery Lessons Instead of
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There is a solution to this problem
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jQuery provides a secondary way of
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Lesson 3: Callback Functions All jQ
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For example, the following statemen
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As you may know an object can conta
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Notice that when we do it this way,
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Alternatively, we can create the pa
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if (“light”.match(/darkness/) =
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jQuery and Regular Expressions In p
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This is probably as simple as it ge
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The following example will demonstr
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Making Good CSS Buttons This tutori
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Sometimes it makes sense to make th
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1. Specify javascript: return false
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Our goal is to match the button wit
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So far, we have briefly discussed t
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Note from the Author Looks like you
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