background preloader

Prototypal Inheritance

Prototypal Inheritance
Douglas Crockford www.crockford.com Five years ago I wrote Classical Inheritance in JavaScript (Chinese Italian Japanese). It showed that JavaScript is a class-free, prototypal language, and that it has sufficient expressive power to simulate a classical system. My journey was circuitous because JavaScript itself is conflicted about its prototypal nature. new () produces a new object that inherits from .prototype This indirection was intended to make the language seem more familiar to classically trained programmers, but failed to do that, as we can see from the very low opinion Java programmers have of JavaScript. Fortunately, it is easy to create an operator that implements true prototypal inheritance. function object(o) { function F() {} F.prototype = o; return new F(); } The object function untangles JavaScript's constructor pattern, achieving true prototypal inheritance. So instead of creating classes, you make prototype objects, and then use the object function to make new instances. Related:  Javascript / PatternsProgramming

Prototype-based programming A fruit bowl serves as one example. A "fruit" object would represent the properties and functionality of fruit in general. A "banana" object would be cloned from the "fruit" object, and would also be extended to include general properties specific to bananas. Each individual "banana" object would be cloned from the generic "banana" object. Design and implementation[edit] Prototypal inheritance in JavaScript is described by Douglas Crockford as: you make prototype objects, and then ... make new instances. Almost all prototype-based systems are based on interpreted and dynamically typed languages. Object construction[edit] Systems that support ex nihilo object creation allow new objects to be created from scratch without cloning from an existing prototype. This example in JS 1.8.5 + ( see ) Delegation[edit] Concatenation[edit] Criticism[edit] Languages supporting prototype-based programming[edit] References[edit] Jump up ^ Crockford, Douglas.

Private Members in JavaScript Douglas Crockford www.crockford.com JavaScript is the world's most misunderstood programming language. Some believe that it lacks the property of information hiding because objects cannot have private instance variables and methods. But this is a misunderstanding. JavaScript objects can have private members. Here's how. Objects JavaScript is fundamentally about objects. If a value is a function, we can consider it a method. Objects can be produced by constructors, which are functions which initialize objects. Public The members of an object are all public members. In the constructor This technique is usually used to initialize public instance variables. function Container(param) { this.member = param; } So, if we construct a new object var myContainer = new Container('abc'); then myContainer.member contains 'abc'. In the prototype This technique is usually used to add public methods. Container.prototype.stamp = function (string) { return this.member + string; } So, we can invoke the method Private

Prototypal Inheritance Explained Newcomers to JavaScript often misunderstand its object oriented style. Inheritance, in particular, seems foreign to people coming from other object oriented languages like C++ or Java. When I was new to JavaScript, I tried to manipulate the language to fit the style I already knew. But there's a better way. A Different Style C++ and Java are class-based languages. JavaScript is a prototypal language. We start with a function. function Person(name, age) { if (Boolean(name)) this.name = name; if (Boolean(age)) this.age = age; } The function above will be called to initialize new objects. Let's add some functions and properties to be shared among every new Person object. Now let's initialize two new Person objects. var jane = new Person("Jane Smith", 35); var noName = new Person(); noName.setAge(29); The object structure we get looks like this: diagram 1. When we access a property in jane or in noName or in any other new Person object, JavaScript will check in that object first. Success!

Underscore.js closure-compiler - Closure Compiler Closure Compiler Closure Compiler is a JavaScript optimizing compiler. It parses your JavaScript, analyzes it, removes dead code and rewrites and minimizes what's left. It also checks syntax, variable references, and types, and warns about common JavaScript pitfalls. Try it out! It's easy to try the compiler through our web application at Get the Compiler Download the compiler at or using Maven. The zip file contains a README with quick instructions to get you started. User Documentation You can read more about Closure Compiler at We also have a few low-key wiki pages at Developer Documentation The Closure Compiler javadocs are available at You can browse the source at We accept patches :)

Understanding JavaScript Prototypes. (en Español, русском, 中文) JavaScript’s prototype object generates confusion wherever it goes. Seasoned JavaScript professionals, even authors frequently exhibit a limited understanding of the concept. What is a prototype? A prototype is an object from which other objects inherit properties Can any object be a prototype? Yes. Which objects have prototypes? Every object has a prototype by default. OK back up, what is an object again? An object in JavaScript is any unordered collection of key-value pairs. You said every object has a prototype. Forget everything you learned about the prototype property – it’s probably the biggest source of confusion about prototypes. Ok fine, but false is a primitive, so why does false. When a primitive is asked for it’s prototype it will be coerced to an object. I want to use prototypes for inheritance. But the real power of prototype is seen when multiple instances share a common prototype. So is this where constructors come in? Yes. OK. Example please? Like this:

Static variables Javascript Arrays – passing by reference or by value? – Oren Farhi – Thoughts On Javascript and Development I stumbled across a great article about javascript arrays – Mastering Javascript Arrays. One fact that i didn’t realize until reading this article is that if you pass an array to a function – it is passed by reference by default. Actually, any non primitive object is passed by reference. Array By Reference Basically it means that if you make any changes to the array inside the function, these changes are saved in the original array so you don’t have to “return myArray” at the end of this function (or at any other return statement inside this function) – that’s what’s so great about javascript – being dynamic enough and consolidate various tricks from other low-level languages. var a= [3, 'my new post', {345}] function renderData(a) { a.push(4); } renderData(a); alert(a); // will output the new a - [3, 'my new post', {345}, 4] Array By Value

JavaScript variable name validator Wondering if you can use a given string as a variable name in JavaScript? Learn how it works, or just use this tool. <strong>To use this tool, please <a href= JavaScript</a> and reload the page.</strong> permalink That’s a valid identifier according to ECMAScript 5.1 / Unicode 6.2. However, the NaN, Infinity, and undefined properties of the global object are immutable or read-only. However, web browsers are supposed to support it, as long as at least one character is escaped using a Unicode escape sequence.

Related: