Javascript Best Practices

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BUENAS PRÁCTICAS! EN JAVASCRIPT @jonalvarezz

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'5' - 3

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'5' - 3 2

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'5' + + '5'

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'5' + + '5' '55'

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'foo' + + 'foo'

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'foo' + + 'foo' 'fooNaN'

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'5' + - + - - + - - + + - + - + - - - '3'

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'5' + - + - - + - - + + - + - + - - - '3' '53'

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QUE GONORREA OME

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BMBOHVBHF XJUIFOPSNPVT expresiveQPXFS Douglas Crockford

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Semicolon Except: for, function, if, switch, try and while

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return! {! status: true! };

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return {! status: true! };

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No content

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Floating Points

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0.1 + 0.2

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0.1 + 0.2 0.30000000000000004 IEEE Standard for Binary Floating-Point Arithmetic

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0.1 + 0.2 0.30000000000000004 IEEE Standard for Binary Floating-Point Arithmetic Use integer arithmetic in ﬂoating

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(0.1 + 0.2)*100 30/100 0.3

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parseInt()

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parseInt("43");! // 43! ! parseInt("43 km");! // 43!

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parseInt("09");! // 0! ! parseInt("09", 10);! // 9!

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parseInt("09");! // 0! ! parseInt("09", 10);! // 9!

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parseInt("09");! // 0! ! parseInt("09", 10);! // 9!

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parseInt("09");! // 0! ! parseInt("09", 10);! // 9!

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parseInt("09");! // 0! ! parseInt("09", 10);! // 9! "-8":464&5)&3"%*9 1"3".&5&3

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Equality Operators == and !=

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'' == '0'! // false! ! 0 == '0'! // true! !

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false == 'false'! // false! ! false == '0'! // true! !

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'\t\r\n ' == 0! // true! !

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'\t\r\n ' == 0! // true! !

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Use! === and !==

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NaN Not a Number

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+ "0";! // 0! ! ! + "foo";! // NaN

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NaN === NaN! // false! ! ! NaN !== NaN! // true

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isNaN("I'm a NaN")! // true

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*DPVMECFBCFUUFS QSPHSBNNFSCZVTJOH POMZUIFgood partsBOE BWPJEJOHUIFbad parts Douglas Crockford

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Global variables The worst JavaScript's feature

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var foo = "value";! ! var moo = function() {! ! foo = "Change global";! } // Place a var statement! // outside of any function

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window.foo = "value"; // Defining direct to global object

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foo = "value"; // Implied global

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"-8":464& VARIABLE STATEMENT var foo = "value";

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var moo = function() {! ! ! var foo = "yay!";! ! // ....! ! } // The right way

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var MYAPP = {};! ! var MYAPP.author = {! "first-name" : "Jonathan",! "username" : "@jonalvarezz"! };! ! var MYAPP.speakAt = {! "name" : "PereiraJS",! "location" : "Pereira"! };! // Need globals?

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#&55&3

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Functions

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function moo() {! ! } // function statement var moo = function() {! ! } // function expression

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moo(); // Prints "foo"! ! function moo() {! ! console.log("foo");! } // function statement! // defined at run-time

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moo(); // Error! ! var moo = function() {! ! console.log("foo");! } // function expression! // defined at parse-time

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if (true) { ! ! function foo() {! ! ! return 1;! }! }! else { ! ! function foo() {! ! ! return 2;! }! }! ! foo(); ! // function statement

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if (true) { ! ! function foo() {! ! ! return 1;! }! }! else { ! ! function foo() {! ! ! return 2;! }! }! ! foo(); // 2 ! // function statement

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var foo;! ! if (true) { ! ! foo = function() {! ! ! return 1;! }! }! else { ! ! foo = function() {! ! ! return 2;! }! }! ! foo(); // 1 ! // function expression

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var myMath = {! ! add: function( a, b ) {! ! ! return a + b;! ! }! };! ! myMath.add( 2, 4 ); // 6 ! // function expression

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'*345$-"44'6/$5*0/4 A function is an "Object"

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'*345$-"44'6/$5*0/4 A function is an "Object"

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var moo = function() {! ! // yay!! } // function expression

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(function() {! ! ! ! 'use strict';! ! ! var a, b, c;! ! ! // ...! ! })(); // function statement! // Anonymous function! // Self invoked function

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Scope

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! var foo = function() {! ! var a = 3, b = 5;! ! ! var bar = function() {! ! ! var b = 7, c = 11;! ! ! ! a += b + c;! ! };! ! ! bar();! ! ! return a;! }

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! var foo = function() {! ! var a = 3, b = 5;! ! ! var bar = function() {! ! ! var b = 7, c = 11;! ! ! ! a += b + c;! ! };! ! ! bar();! ! ! return a;! } // 21

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! var foo = function() {! ! var a = 3, b = 5;! ! ! var bar = function() {! ! ! var b = 7, c = 11;! ! ! ! a += b + c;! ! };! ! ! bar();! ! ! return a;! } // 21 Function Scope!

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Closures

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* CODES *

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Modules

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"NPEVMFJTBGVODUJPO PSPCKFDUUIBUQSFTFOUT BOEJOUFSGBDFCVUUIBU hides its state and implementation

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var sm = seria_maker();! ! sm.set_prefix('Q');! ! sm.set_seq(1000);! ! var unique = sm.gensym();! ! // Q1000 // Object that generates uniques strings