Javascript patterns
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The document discusses JavaScript as a language. It notes that JavaScript implements ECMAScript and is object-oriented without classes. Objects are dynamic collections of named properties that can be added, removed or updated. JavaScript also has loose typing, lambdas, native and host objects, and prototypical inheritance. Good parts of the language include lambdas, dynamic objects, loose typing and object literals, while bad parts include global variables, addition/concatenation with +, semicolon insertion, typeof, with and eval, and comparisons with == and !=. The document then covers general patterns in JavaScript including minimizing globals, implied globals, the single var pattern, namespacing, and more.
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Javascript patterns
- 1. JavaScript -‐ What’s in the language?
- 2. JavaScript as a language • Implementa3on of ECMASCRIPT • Object oriented • No Classes • Dynamic Objects -‐ collec3on of named proper3es. You can add, remove, update its members. • Loose typing • lambdas • Na3ve and host objects -‐ Environment specific • Prototypical inheritance
- 3. Good Parts • Lambda • Dynamic objects • Loose typing • Object literals
- 4. Bad Parts • Global Variables • + adds and concatenates • Semicolon inser3on • typeof • with and eval • == and != • false, null, undefined, NaN
- 6. Minimizing global variables /*#Title:#Minimizing#Globals#Description:#they#are#declared#outside#of# function#or#simply#used#without#being#declared! */! myglobal!=!"hello";!//#antipattern! console.log(myglobal);!//#"hello"! console.log(window.myglobal);!//#"hello"! console.log(window["myglobal"]);!//#"hello"! console.log(this.myglobal);!//#"hello"!
- 7. Implied global variables ! //!antipatten!1! ! function!sum(x,!y)!{! ! ! //!implied!global! ! ! result!=!x!+!y;! ! ! return!result;! ! }! ! //!preferred!1! ! function!sum(x,!y)!{! //!a!variable!declared!inside!of!a!function!is!local!to!that!function!and!not! available!outside!the!function! ! ! var!result!=!x!+!y;! ! ! return!result;! ! }!
- 8. ! //"antipattern"2! ! function!foo()!{! ! ! var!a!=!b!=!0;! ! ! //"...! ! }! ! //"the"preceding"code"snippet"will"behave"as"if"you've"typed"the"following! ! var!a!=!(b!=!0);! ! //"preferred"2! ! function!foo()!{! ! ! var!a,!b;! ! ! //"...! ! ! a!=!b!=!0;!//"both"local! ! }!
- 9. Single var PaSern ! ! /*!Benefits:! !*!1.!Provides!a!single!place!to!look!for!all!the!local!variables!needed!by!the! function! ! !*!2.!Prevents!logical!errors!when!a!variable!is!used!before!it's!defined! ! !*!3.!Helps!you!remember!to!declare!variables!and!therefore!minimize!globals! ! */! ! function!func()!{! ! ! var!a!=!1,! ! ! ! ! b!=!2,! ! ! ! ! sum!=!a!+!b,! ! ! ! ! myobject!=!{},! ! ! ! ! i,! ! ! ! ! j;! ! ! //!function!body...! ! }! ! function!updateElement()!{! ! ! var!el!=!document.getElementById("result"),! ! ! ! ! style!=!el.style;! ! ! //!do!something!with!el!and!style...! ! }!
- 10. Namespacing ! //!unsafe! ! var!MYAPP!=!{};! ! //!better! ! if!(typeof!MYAPP!===!"undefined")!{! ! ! var!MYAPP!=!{};! ! }! ! //!or!shorter! ! var!MYAPP!=!MYAPP!||!{};!
- 11. ! MYAPP.namespace!=!function!(ns_string)!{! ! ! var!parts!=!ns_string.split('.'),! ! ! ! ! parent!=!MYAPP,! ! ! ! ! i;! ! ! //"strip"redundant"leading"global! ! ! if!(parts[0]!===!"MYAPP")!{! ! ! ! parts!=!parts.slice(1);! ! ! }! ! ! for!(i!=!0;!i!<!parts.length;!i!+=!1)!{! ! ! ! //"create"a"property"if"it"doesn't"exist! ! ! ! if!(typeof!parent[parts[i]]!===!"undefined")!{! ! ! ! ! parent[parts[i]]!=!{};! ! ! ! }! ! ! ! parent!=!parent[parts[i]];! ! ! }! ! ! return!parent;! ! };! ! //"assign"returned"value"to"a"local"var! ! var!module2!=!MYAPP.namespace('MYAPP.modules.module2');! ! console.log(module2!===!MYAPP.modules.module2);!//"true!
- 12. Implied Typecas3ng: false, null, undefined, NaN ! var!zero!=!0;! ! /*#antipattern! # #*#JavaScript#implicitly#typecasts#variables#when#you#compare#them.! # #*#That's#why#comparisons#such#as#false#==#0#or#""#==#0#return#true.! # #*/! ! if!(zero!==!false)!{! ! ! //#this#block#is#executed...! ! }! ! //#preferred! ! /*#To#avoid#confusion#caused#by#the#implied#typecasting,! *#always#use#the#===#and#!==#operators#that#check#both#the#values#and#the#type#of# the#expressions#you#compare! # */! ! if!(zero!===!false)!{! ! ! //#not#executing#because#zero#is#0,#not#false! ! }!
- 15. For-‐in loops ! /*#Title:#for-in#loops! # #*#Description:#optimized#for-in#loops! # #*/! ! //#the#object! ! var!man!=!{! ! ! hands:2,! ! ! legs:2,! ! ! heads:1! ! };! ! //#somewhere#else#in#the#code! ! //#a#method#was#added#to#all#objects! ! if!(typeof!Object.prototype.clone!===!'undefined')!{! ! ! Object.prototype.clone!=!function!()!{! ! ! };! ! }!
- 16. ! //"antipattern! ! //"for,in"loop"without"checking"hasOwnProperty()! ! for!(var!i!in!man)!{! ! ! console.log(i,!":",!man[i]);! ! }! ! /*! " "*"result"in"the"console! " "*"hands":"2! " "*"legs":"2! " "*"hands":"1! " "*"clone:"function()! " "*/! ! //"preferred"1! ! for!(var!i!in!man)!{! ! ! if!(man.hasOwnProperty(i))!{!//"filter! ! ! ! console.log(i,!":",!man[i]);! ! ! }! ! }! ! /*! " "*"result"in"the"console! " "*"hands":"2! " "*"legs":"2! " "*"heads":"1! " "*/!
- 17. Automa3c semicolon inser3on //antipattern! return! {! !!!!status:!true! };! ! //preferred! return{! !!!!status:!true! };! !
- 18. Func:on Pa8erns
- 19. Closures //"Your"setup"function"can"store"some"private"data"in"a"closure"and"use"that"data" somehow.! //"Here"setup()"creates"a"counter"function,"which"gives"a"next"ID"for"example." But"the"count"variable"is"not"exposed.! var!setup!=!function!()!{! ! var!count!=!0;! ! return!function!()!{! ! ! return!++count;! ! };! };! //"usage! var!next!=!setup();! //next();"//"returns"1! //next();"//"returns"2! //next();"//"returns"3!
- 20. Currying /***! #currying! #***/! //#a#curried#add()! //#accepts#partial#list#of#arguments! function!add(x,!y)!{! ! var!oldx!=!x,!oldy!=!y;! ! if!(typeof!oldy!===!"undefined")!{!//#partial! ! ! return!function!(newy)!{! ! ! ! return!oldx!+!newy;! ! ! }! ! }! ! //#full#application! ! return!x!+!y;! }! //#test! typeof!add(5);!//#"function"! add(3)(4);!//#7!
- 21. Literals, Constructors and Object crea:on Pa8erns
- 22. To ‘new’ or not ! ! ! ! //!antipattern! ! var!car!=!new!Object();! ! car.goes!=!"far";! ! //!preferred! ! var!car!=!{goes:"far"};! ! //!constructor! ! function!Waffle()!{! ! ! this.tastes!=!"yummy";! ! }! ! //!antipattern! ! //!forgotten!`new`! ! var!good_morning!=!Waffle();! ! console.log(typeof!good_morning);!//!"undefined"! ! console.log(window.tastes);!//!"yummy"! ! //!preferred! ! var!good_morning!=!new!Waffle();! ! console.log(typeof!good_morning);!//!"object"! ! console.log(good_morning.tastes);!//!"yummy"!
- 23. PaSerns for enforcing ‘new’ ! function!Waffle()!{! ! if!(!(this!instanceof!Waffle))!{! ! ! return!new!Waffle();! ! }! ! this.tastes!=!"yummy";! }! var!good_morning!=!new!Waffle();! var!good_evening!=!Waffle();! console.log(typeof!good_morning);!//""object"! console.log(good_morning.tastes);!//""yummy"! console.log(typeof!good_evening);!//""object"! console.log(good_evening.tastes);!//""yummy"!
- 24. ! //!antipattern! ! //!with!wrappers! ! var!s!=!new!String("my!string");! ! var!n!=!new!Number(101);! ! var!b!=!new!Boolean(true);! ! //!preferred! ! //!without!wrappers! ! var!s!=!"my!string";! ! var!n!=!101;! ! var!b!=!true;!
- 26. Module paSern MYAPP.utilities.array/=/(function/()/{/ / / / / //"private"properties/ / / / / var/array_string/=/"[object/Array]",/ / / / / ops/=/Object.prototype.toString,/ / / / / / //"private"methods/ / / / / inArray/=/function/(haystack,/needle)/{/ / / / / / for/(var/i/=/0,/max/=/haystack.length;/i/</max;/i/+=/1)/ / / / / / / if/(haystack[i]/===/needle)/{/ / / / / / / / return/i;/ / / / / / / }/ / / / / / }/ / / / / / return//1;/ / / / / },/ / / / / isArray/=/function/(a)/{/ / / / / / return/ops.call(a)/===/array_string;/ / / / / };/ / / / / //"end"var/ / / / / / //"revealing"public"API/ / / / / return/{/ / / / / / isArray:isArray,/ / / / / / indexOf:inArray/ / / / / };/ / / / }());/ !
- 28. Prototypal Inheritance ! function!object(o)!{! ! ! function!F()!{! ! ! }! ! ! F.prototype!=!o;! ! ! return!new!F();! ! }! ! //"object"to"inherit"from! ! var!parent!=!{! ! ! name:"Papa"! ! };! ! //"the"new"object! ! var!child!=!object(parent);! ! //"testing! ! console.log(child.name);!//""Papa"!
- 29. //"parent"constructor! function!Person()!{! ! //"an""own""property! ! this.name!=!"Adam";! }! //"a"property"added"to"the"prototype! Person.prototype.getName!=!function!()!{! ! return!this.name;! };! //"create"a"new"person! var!papa!=!new!Person();! //"inherit! var!kid!=!object(papa);! //"test"that"both"the"own"property! //"and"the"prototype"property"were"inherited! console.log(kid.getName());!//""Adam"!
- 30. Augmen3ng built-‐in Prototypes if!(typeof!Object.prototype.myMethod!!==!"function")!{! ! Object.prototype.myMethod!=!function!()!{! ! ! //"implementation...! ! };! }!
- 31. Design Pa8erns
- 32. CREATIONAL Builder constructs complex objects by separa3ng construc3on and representa3on Factory Method creates objects without specifying the exact class to create Singleton restricts object crea3on for a class to only one instance STRUCTURAL Decorator dynamically adds/overrides behavior in an exis3ng method of an object Facade provides a simplified interface to a large body of code BEHAVIORAL Chain of responsibility delegates commands to a chain of processing objects Command creates objects which encapsulate ac3ons and parameters Mediator allows loose coupling between classes by being the only class that has detailed knowledge of their methods Observer is a publish/subscribe paSern which allows a number of observer objects to see an event
- 36. AMD -‐ Asynchronous module defini3on define(' ''''module_id'/*optional*/,' ''''[dependencies]'/*optional*/,' ''''definition' function'/*function-for-instantiating-the-module-or-object*/' )' ! ! ! require(["foo",'"bar"],'function'(foo,'bar)'{' ''''//-rest-of-your-code-here' ''''foo.doSomething();' });' !
- 37. Prolifera3on of MV* frameworks
- 38. Prolifera3on of MV* frameworks • Rich internet single page applica3ons • Data Binding • Client side templates • Client-‐Centric or Server-‐Centric-‐ that is the ques3on.
- 39. • Minify, concatenate, compress • Load scripts at the end of pages • Sta3c code analysis using Jslint/Jshint • Tes3ng your code – Jasmine, Phantomjs etc
- 40. References
- 41. Ques:ons?