03 Advanced JavaScript

Advanced JavaScript From Novice To Ninja Tuesday, September 18, 12

Agenda JavaScript History Language Overview Arrays & Objects Functions Tuesday, September 18, 12

The World’s Most Misunderstood Programming Language Tuesday, September 18, 12

History 1995 Brendan Eich started developing a new language for Netscape Navigator 2.0 Original name was LiveScript Announced on Dec 1995 as JavaScript 1996 Microsoft responded with JScript Tuesday, September 18, 12

JS Today Used for Client side development on desktop and mobile Used for Server side development using NodeJs Embedded in applications using Rhino Tuesday, September 18, 12

Language Overview JavaScript is not a toy JavaScript has nothing to do with Java JavaScript is a powerful programming language on its own Tuesday, September 18, 12

JavaScript Key Ideas Interpreter based (no compilation) Loosely typed language Objects are just hash tables Prototypical inheritance model Functions are regular objects (with a twist) Arrays are regular objects (with a twist) Tuesday, September 18, 12

JavaScript Core Types Numbers Strings Booleans null undeﬁned Objects Tuesday, September 18, 12

JavaScript Gotchas var x = “3”; var y = 5; x + y == 8; x + y == 35; x + y === 35; Tuesday, September 18, 12

JavaScript Gotchas var x = “3”; var y = 5; x + y == 8; // false x + y == 35; // true x + y === 35; // false Tuesday, September 18, 12

JavaScript Gotchas function foo() { function bar() { return return { val : 3 } } { var x = foo(); val : 3 } var y = bar(); } x.val == y.val; Tuesday, September 18, 12

JavaScript Gotchas // returns undef // returns object function foo() { function bar() { return return { val : 3 } } { var x = foo(); val : 3 } var y = bar(); } x.val == y.val; // error Tuesday, September 18, 12

JavaScript Gotchas 1 === 1; 1/0 === 1/0; Number(‘a’) === Number(‘a’); ‘a‘ === “a” Tuesday, September 18, 12

JavaScript Gotchas 1 === 1; // true 1/0 === 1/0; // true Number(‘a’) === Number(‘a’); // false ‘a‘ === “a” // true Tuesday, September 18, 12

Q&A JavaScript History Language Overview Arrays & Objects Functions Tuesday, September 18, 12

Objects JS Objects are container for data A data ﬁeld in an object is a name-value pair The name can be any string The value can be anything except undeﬁned Tuesday, September 18, 12

Using Objects name Ynon Perek website http://www.ynonperek.com Tuesday, September 18, 12

Using Objects var myObject = { name : “Ynon Perek”, website : “http://www.ynonperek.com” } Tuesday, September 18, 12

Using Objects console.dir(myObject); // prints all the fields myObject.name === “Ynon Perek” myObject[‘website’] === http://www.ynonperek.com Tuesday, September 18, 12

Object Patterns Object Literals vs. Object Ctor Maker functions Object Prototypes Tuesday, September 18, 12

Object Literals vs. Ctor Using object literals is the recommended way to create objects It is faster than calling new Object() It is more predictable than calling new Object() It is simpler Tuesday, September 18, 12

Maker Functions Tuesday, September 18, 12

Maker Functions function Person(name, age) { var that = { name : name, age : age }; that.hello = function() { console.log(“Hello, My name is ” + that.name) }; return that; } Tuesday, September 18, 12

Maker Functions Using a maker function to create new objects saves duplicate code Use the “that” pattern against “new” pitfalls Load your newly created object with functions Tuesday, September 18, 12

Example Implement a Quiz JavaScript system Use “Question” class with four possible answers and on correct answer Use “Quiz” class to hold an array of questions Tuesday, September 18, 12

Object Prototypes Tuesday, September 18, 12

Object Prototypes In JavaScript, every object has a “prototype” object. When JS interpreter fails to ﬁnd an attribute in an object, it searches the prototype. Tuesday, September 18, 12

Prototype Chain Freshman Student Person goto: party grade : 90 age : 12 Freshman.grade === 90 // from Student Student.age === 12 // from Person Worker.age === 12 // from Person Worker Worker.salary === 3800 // from Worker salary : 3800 Tuesday, September 18, 12

The object Function function object(parent) { function F() {}; F.prototype = parent || Object; return new F(); } Tuesday, September 18, 12

The object Function creates a new object with the prototype ‘parent’ uses new to keep the prototype link supports no arguments for object literals Tuesday, September 18, 12

Prototype Example var person = { age : 12 }; var student = object(person); student.grade = 90; var freshman = object(student); freshman.goto = “party”; Tuesday, September 18, 12

Prototypes & Makers Always use Maker functions For leafs, initialize object literals For nodes, use the object() function Tuesday, September 18, 12

Exercise Write a maker function for a Car object, using an object literal. Car should provide members: max_speed and drive() Write maker functions for 3 car models using the object() function. Implement a function on a car model which uses data from Car Tuesday, September 18, 12

Arrays Arrays are objects with numeric keys. A length attribute is maintained automatically by JS to mean last_index + 1 Tuesday, September 18, 12

Array Functions join pop, push shift, unshift reverse, sort - changes original array a.slice(0, a.length).reverse() - Does not modify original array a Tuesday, September 18, 12

Exercise Implement a Phonebook object that maintains an array of Contact objects. Each Contact should have a name ﬁeld and a phone ﬁeld. Test by creating 5 contacts in the Phonebook and print them to the console. Tuesday, September 18, 12

Functions The word ‘function’ Followed by an optional name Followed by a set of parameters Followed by the function body Tuesday, September 18, 12

Functions function hello(who) { console.log(“Hello, “ + who); } var hello = function hello(who) { console.log(“Hello, “ + who); }; Tuesday, September 18, 12

Function.Prototype apply, call toString Tuesday, September 18, 12

Scope In JavaScript, only functions have scope. The var keyword indicates a scoped variable There is no block scope Tuesday, September 18, 12

Scope // Using functions to scope our code (function() { var x = 5; var y = 7; console.log(x + y); }()); Tuesday, September 18, 12

Scope Do: Wrap every ﬁle in an anonymous function Preﬁx every variable with var A Good fence makes good neighbors Tuesday, September 18, 12

Constructor Functions If a function is called with new: A new object is created before entering the function That object is passed as the this argument That object becomes the default return value of the function Tuesday, September 18, 12

Return Value return is used to return a value default return value for non-ctor functions is undeﬁned default return value for ctor is this Tuesday, September 18, 12

Tip Prefer that-style constructor over this In that-style constructors, always remember to return that. Tuesday, September 18, 12

Function Patterns Modules Immediate Functions Conﬁguration Objects Prototype Methods Tuesday, September 18, 12

Modules A module is a unit of code reuse Some code in a module is “public” - shared with other modules. Some code in a module is “private” - cannot be accessed from outside. Tuesday, September 18, 12

Function Arguments function sum() { var i = 0, n = arguments.length, sum = 0; for ( i=0; i < n; ++i ) { sum += arguments[i]; } return sum; } Tuesday, September 18, 12

Example - Calculator Public code: add_to_register sub_from_register read_register zero_register http://ynonperek.com/course/web/javascript- functions.html#modules Tuesday, September 18, 12

Immediate Functions Execute a function as soon as it is deﬁned Provides a scoped “sandbox” for initialization code Pass in the global object to avoid using ‘window’ in your code. Tuesday, September 18, 12

Configuration Objects When a large list of arguments is required, use configuration objects Solves “which comes first” Rule of Thumb: if params > 2, use the object Tuesday, September 18, 12

Conﬁguration Objects Example Student function which takes a conﬁguration object with optional values http://ynonperek.com/course/web/javascript- functions.html#conf Tuesday, September 18, 12

Function Exercise Write a module for time management Module should provide: add_meeting(meeting_info) delete_meeting(meeting_info) get_meetings_between(start_dt, end_dt) Tuesday, September 18, 12

Function Prototypes Tuesday, September 18, 12

Function Prototypes functions have a special attribute: prototype When an object’s attribute lookup is performed, the interpreter checks its constructor.prototype Tuesday, September 18, 12

Function Prototypes We implement inheritance using prototypes - this is called prototypical inheritance Example: http://ynonperek.com/course/fed/ javascript-oo.html Tuesday, September 18, 12

Design Patterns Singleton Factory Super Tuesday, September 18, 12

Singleton Put the object on global. Access it from everywhere in your program Always consider using a namespace global.Log = log; Tuesday, September 18, 12

Factory Use a single factory object with a method to produce each product Implement a product method that takes a name of a product, and runs its correct producer function CarFactory.produce = function(model) { var ctor = CarFactory[model]; return ctor(); } Tuesday, September 18, 12

Using Super JavaScript has no native ‘super’ call To use the superclass in the inheritance chain, we must work something out ourselves Let’s modify our object function to allow super Tuesday, September 18, 12

Using Super function object(parent) { function F() { /* CODE GOES HERE */ }; F.prototype = parent || Object; return new F(); } Tuesday, September 18, 12

Using Super function object(parent) { function F() { this.uber = parent }; F.prototype = parent || Object; return new F(); } Tuesday, September 18, 12

Using Super Now each object has an ‘uber’ property that points to its prototype object Can use student.uber.age to get the person’s age Tuesday, September 18, 12

JS App Tips App is made of components. On mobile, only one visible component at a time; on Desktop, can have more than one. Each component has its own JS ﬁle Diﬀerent components can communicate using a global object in a private namespace A single controller object moves components in/ out of view Tuesday, September 18, 12

Thank You Ynon Perek ynonperek@yahoo.com ynonperek.com Tuesday, September 18, 12

03 Advanced JavaScript

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