[Translation] JavaScript specifications-sunflower collection and javascript sunflower collection

[Translation] JavaScript specifications-sunflower collection and javascript sunflower collection

[Translation] JavaScript Specification

Translation: https://github.com/airbnb/javascript

Type

• Original Value: Equivalent to passing values

stringnumberbooleannullundefinedvar foo = 1,    bar = foo;bar = 9;console.log(foo, bar); // => 1, 9

Complex types: Equivalent to transferring reference

• objectarrayfunctionvar foo = [1, 2],    bar = foo;bar[0] = 9;console.log(foo[0], bar[0]); // => 9, 9

Object

• Create an object using the Literal Value

  // badvar item = new Object();// goodvar item = {};

• Do not use reserved words as the key

  // badvar superman = {  class: 'superhero',  default: { clark: 'kent' },  private: true};// goodvar superman = {  klass: 'superhero',  defaults: { clark: 'kent' },  hidden: true};

Array

• Create an array using the Literal Value

  // badvar items = new Array();// goodvar items = [];

• If you do not know the length of the array, use push

  var someStack = [];// badsomeStack[someStack.length] = 'abracadabra';// goodsomeStack.push('abracadabra');

• Use slice. jsPerf when you need to copy the Array

  var len = items.length,    itemsCopy = [],    i;// badfor (i = 0; i < len; i++) {  itemsCopy[i] = items[i];}// gooditemsCopy = items.slice();

• Use slice to convert the objects of the class array into an array.

  function trigger() {  var args = Array.prototype.slice.call(arguments);  ...}

String

• Use single quotes for strings''

  // badvar name = "Bob Parr";// goodvar name = 'Bob Parr';// badvar fullName = "Bob " + this.lastName;// goodvar fullName = 'Bob ' + this.lastName;

• Character strings with more than 80 characters should use string connection to wrap

• Note: long string connection may affect the performance if it is over-used. jsPerf & Discussion

  // badvar errorMessage = 'This is a super long error that was thrown because of Batman. When you stop to think about how Batman had anything to do with this, you would get nowhere fast.';// badvar errorMessage = 'This is a super long error that \was thrown because of Batman. \When you stop to think about \how Batman had anything to do \with this, you would get nowhere \fast.';// goodvar errorMessage = 'This is a super long error that ' +  'was thrown because of Batman.' +  'When you stop to think about ' +  'how Batman had anything to do ' +  'with this, you would get nowhere ' +  'fast.';

• Use join instead of string join to construct a string during programming, especially IE: jsPerf.

  var items,    messages,    length, i;messages = [{    state: 'success',    message: 'This one worked.'},{    state: 'success',    message: 'This one worked as well.'},{    state: 'error',    message: 'This one did not work.'}];length = messages.length;// badfunction inbox(messages) {  items = '<ul>';  for (i = 0; i < length; i++) {    items += '<li>' + messages[i].message + '</li>';  }  return items + '</ul>';}// goodfunction inbox(messages) {  items = [];  for (i = 0; i < length; i++) {    items[i] = messages[i].message;  }  return '<ul><li>' + items.join('</li><li>') + '</li></ul>';}

<Function

• Function expression:

  // Anonymous function expression var anonymous = function () {return true ;}; // famous function expression var named = function named () {return true ;}; // call the function expression (function () {console. log ('Welcome to the Internet. please follow me. ');})();

• Never declare a function in a non-function block and assign that function to a variable. The Browser allows you to do this, but the parsing is different.

• Note:ECMA-262 DefinitionBlockIt is defined as a set of statements, and the function declaration is not a statement. Read the ECMA-262's explanation of this problem.

  // badif (currentUser) {  function test() {    console.log('Nope.');  }}// goodif (currentUser) {  var test = function test() {    console.log('Yup.');  };}

• Never name a parameterargumentsThis will pass over the function scope.argumentsObject.

  // badfunction nope(name, options, arguments) {  // ...stuff...}// goodfunction yup(name, options, args) {  // ...stuff...}

Attribute

• Brackets are used to access attributes using variables.

  var luke = {  jedi: true,  age: 28};function getProp(prop) {  return luke[prop];}var isJedi = getProp('jedi');

Variable

• Always usevarTo declare variables. If you do not do so, global variables will be generated. We must avoid contamination of the global namespace.

  // badsuperPower = new SuperPower();// goodvar superPower = new SuperPower();

• Use onevarMultiple variables are declared in the new line, and four spaces are indented.

  // badvar items = getItems();var goSportsTeam = true;var dragonball = 'z';// goodvar items = getItems(),    goSportsTeam = true,    dragonball = 'z';

• Finally, declare unassigned variables. It is useful when you want to reference previously assigned variables.

  // badvar i, len, dragonball,    items = getItems(),    goSportsTeam = true;// badvar i, items = getItems(),    dragonball,    goSportsTeam = true,    len;// goodvar items = getItems(),    goSportsTeam = true,    dragonball,    length,    i;

• Declare variables at the top of the scope to avoid issues related to variable declaration and assignment.

  // badfunction() {  test();  console.log('doing stuff..');  //..other stuff..  var name = getName();  if (name === 'test') {    return false;  }  return name;}// goodfunction() {  var name = getName();  test();  console.log('doing stuff..');  //..other stuff..  if (name === 'test') {    return false;  }  return name;}// badfunction() {  var name = getName();  if (!arguments.length) {    return false;  }  return true;}// goodfunction() {  if (!arguments.length) {    return false;  }  var name = getName();  return true;}

Conditional expressions and equal signs

• Proper Use===And!==And==And!=.

• The forced type conversion of conditional expressions follows the following rules:

  • ObjectCalculatedTrue
  • UndefinedCalculatedFalse
  • NullCalculatedFalse
  • Boolean ValueCalculatedBoolean Value
  • NumberIf yes+ 0,-0, or NaNCalculatedFalseOtherwiseTrue
  • StringIf it is a Null String''Is calculatedFalseOtherwiseTrue

  if ([0]) {  // true  // An array is an object, objects evaluate to true}

• Use shortcuts.

  // badif (name !== '') {  // ...stuff...}// goodif (name) {  // ...stuff...}// badif (collection.length > 0) {  // ...stuff...}// goodif (collection.length) {  // ...stuff...}

• Learn more about Truth Equality and JavaScript

Block

• Use braces for all multiline Blocks

  // badif (test)  return false;// goodif (test) return false;// goodif (test) {  return false;}// badfunction() { return false; }// goodfunction() {  return false;}

Note

• Use/** ... */Comments on multiple lines, including descriptions, specified types, parameter values, and returned values

  // bad// make() returns a new element// based on the passed in tag name//// @param <String> tag// @return <Element> elementfunction make(tag) {  // ...stuff...  return element;}// good/** * make() returns a new element * based on the passed in tag name * * @param <String> tag * @return <Element> element */function make(tag) {  // ...stuff...  return element;}

• Use//Comment on a single line, comment on a single line on the comment object, and put a blank line before the comment.

  // badvar active = true;  // is current tab// good// is current tabvar active = true;// badfunction getType() {  console.log('fetching type...');  // set the default type to 'no type'  var type = this._type || 'no type';  return type;}// goodfunction getType() {  console.log('fetching type...');  // set the default type to 'no type'  var type = this._type || 'no type';  return type;}

• If you have a problem that you need to review or if you suggest a solution that needs to be implemented, you need to add a comment before you.FIXMEOrTODOHelp Others quickly understand

  function Calculator() {  // FIXME: shouldn't use a global here  total = 0;  return this;}function Calculator() {  // TODO: total should be configurable by an options param  this.total = 0;  return this;}

Blank

• Set tab to 4 spaces

  // badfunction() {∙∙var name;}// badfunction() {∙var name;}// goodfunction() {∙∙∙∙var name;}

• Place a space in front of the braces

  // badfunction test(){  console.log('test');}// goodfunction test() {  console.log('test');}// baddog.set('attr',{  age: '1 year',  breed: 'Bernese Mountain Dog'});// gooddog.set('attr', {  age: '1 year',  breed: 'Bernese Mountain Dog'});

• Use indentation for long method chains.

  // bad$('#items').find('.selected').highlight().end().find('.open').updateCount();// good$('#items')  .find('.selected')    .highlight()    .end()  .find('.open')    .updateCount();// badvar leds = stage.selectAll('.led').data(data).enter().append('svg:svg').class('led', true)    .attr('width',  (radius + margin) * 2).append('svg:g')    .attr('transform', 'translate(' + (radius + margin) + ',' + (radius + margin) + ')')    .call(tron.led);// goodvar leds = stage.selectAll('.led')    .data(data)  .enter().append('svg:svg')    .class('led', true)    .attr('width',  (radius + margin) * 2)  .append('svg:g')    .attr('transform', 'translate(' + (radius + margin) + ',' + (radius + margin) + ')')    .call(tron.led);

Comma

• Do not put commas in front

  // badvar once  , upon  , aTime;// goodvar once,    upon,    aTime;// badvar hero = {    firstName: 'Bob'  , lastName: 'Parr'  , heroName: 'Mr. Incredible'  , superPower: 'strength'};// goodvar hero = {  firstName: 'Bob',  lastName: 'Parr',  heroName: 'Mr. Incredible',  superPower: 'strength'};

• Do not add extra commas, which may cause errors in IE. If you add one more comma, some ES3 implementations will calculate the length of multiple arrays.

  // badvar hero = {  firstName: 'Kevin',  lastName: 'Flynn',};var heroes = [  'Batman',  'Superman',];// goodvar hero = {  firstName: 'Kevin',  lastName: 'Flynn'};var heroes = [  'Batman',  'Superman'];

Semicolon

• The statement must end with a plus sign.

  // bad(function() {  var name = 'Skywalker'  return name})()// good(function() {  var name = 'Skywalker';  return name;})();// good;(function() {  var name = 'Skywalker';  return name;})();

Type conversion

• Type conversion is performed at the beginning of the statement.

• String:

  //  => this.reviewScore = 9;// badvar totalScore = this.reviewScore + '';// goodvar totalScore = '' + this.reviewScore;// badvar totalScore = '' + this.reviewScore + ' total score';// goodvar totalScore = this.reviewScore + ' total score';

• Use numbersparseIntAnd always carry the base of type conversion.

  var inputValue = '4';// badvar val = new Number(inputValue);// badvar val = +inputValue;// badvar val = inputValue >> 0;// badvar val = parseInt(inputValue);// goodvar val = Number(inputValue);// goodvar val = parseInt(inputValue, 10);// good/** * parseInt was the reason my code was slow. * Bitshifting the String to coerce it to a * Number made it a lot faster. */var val = inputValue >> 0;

• Boolean value:

  var age = 0;// badvar hasAge = new Boolean(age);// goodvar hasAge = Boolean(age);// goodvar hasAge = !!age;

Naming Conventions

• Avoid a single character name and make your variable name descriptive.

  // badfunction q() {  // ...stuff...}// goodfunction query() {  // ..stuff..}

• Use the hump naming rules when naming objects, functions, and instances

  // badvar OBJEcttsssss = {};var this_is_my_object = {};var this-is-my-object = {};function c() {};var u = new user({  name: 'Bob Parr'});// goodvar thisIsMyObject = {};function thisIsMyFunction() {};var user = new User({  name: 'Bob Parr'});

• Use the upper case of the hump when naming constructors or classes

  // badfunction user(options) {  this.name = options.name;}var bad = new user({  name: 'nope'});// goodfunction User(options) {  this.name = options.name;}var good = new User({  name: 'yup'});

• Name a private property with an underline_

  // badthis.__firstName__ = 'Panda';this.firstName_ = 'Panda';// goodthis._firstName = 'Panda';

• When you savethisUse_this.

  // badfunction() {  var self = this;  return function() {    console.log(self);  };}// badfunction() {  var that = this;  return function() {    console.log(that);  };}// goodfunction() {  var _this = this;  return function() {    console.log(_this);  };}

Accessors

• Attribute accessors are not required

• If you do have accessors, use getVal () and setVal ('hello ')

  // baddragon.age();// gooddragon.getAge();// baddragon.age(25);// gooddragon.setAge(25);

• If the attribute is a Boolean value, use isVal () or hasVal ()

  // badif (!dragon.age()) {  return false;}// goodif (!dragon.hasAge()) {  return false;}

• You can create get () and set () functions, but they must be consistent.

  function Jedi(options) {  options || (options = {});  var lightsaber = options.lightsaber || 'blue';  this.set('lightsaber', lightsaber);}Jedi.prototype.set = function(key, val) {  this[key] = val;};Jedi.prototype.get = function(key) {  return this[key];};

Constructor

• Instead of overwriting the prototype with a new object, overwriting the prototype will cause inheritance problems.

  function Jedi() {  console.log('new jedi');}// badJedi.prototype = {  fight: function fight() {    console.log('fighting');  },  block: function block() {    console.log('blocking');  }};// goodJedi.prototype.fight = function fight() {  console.log('fighting');};Jedi.prototype.block = function block() {  console.log('blocking');};

• Method can returnthisThe help method can be chained.

  // badJedi.prototype.jump = function() {  this.jumping = true;  return true;};Jedi.prototype.setHeight = function(height) {  this.height = height;};var luke = new Jedi();luke.jump(); // => trueluke.setHeight(20) // => undefined// goodJedi.prototype.jump = function() {  this.jumping = true;  return this;};Jedi.prototype.setHeight = function(height) {  this.height = height;  return this;};var luke = new Jedi();luke.jump()  .setHeight(20);

• You can write a custom toString () method, but make sure it works normally without any side effects.

  function Jedi(options) {  options || (options = {});  this.name = options.name || 'no name';}Jedi.prototype.getName = function getName() {  return this.name;};Jedi.prototype.toString = function toString() {  return 'Jedi - ' + this.getName();};

Event

• When attaching data to an event, a hash is passed in instead of the original value. This allows later contributors to add more data to the event data, instead of finding and updating the event processor.

  // bad$(this).trigger('listingUpdated', listing.id);...$(this).on('listingUpdated', function(e, listingId) {  // do something with listingId});

  Better:

  // good$(this).trigger('listingUpdated', { listingId : listing.id });...$(this).on('listingUpdated', function(e, data) {  // do something with data.listingId});

Module

• The module should!This ensures that if a faulty module forgets to include the last semicolon, no error will occur after merging.
• This file should be named after the camper and in a folder of the same name, and the exported files must have the same name.
• Add a method named noConflict () to set the exported module to a previous version and return it.

• Always declare at the top of the module'use strict';

  // fancyInput/fancyInput.js!function(global) {  'use strict';  var previousFancyInput = global.FancyInput;  function FancyInput(options) {    this.options = options || {};  }  FancyInput.noConflict = function noConflict() {    global.FancyInput = previousFancyInput;    return FancyInput;  };  global.FancyInput = FancyInput;}(this);

JQuery

• Cache jQuery queries

  // badfunction setSidebar() {  $('.sidebar').hide();  // ...stuff...  $('.sidebar').css({    'background-color': 'pink'  });}// goodfunction setSidebar() {  var $sidebar = $('.sidebar');  $sidebar.hide();  // ...stuff...  $sidebar.css({    'background-color': 'pink'  });}

• Use cascading for DOM queries$('.sidebar ul')Or$('.sidebar ul'), JsPerf

• Usefind

  // bad$('.sidebar', 'ul').hide();// bad$('.sidebar').find('ul').hide();// good$('.sidebar ul').hide();// good$('.sidebar > ul').hide();// good (slower)$sidebar.find('ul');// good (faster)$($sidebar[0]).find('ul');

ECMAScript 5 compatibility

• Refer to ES5 compatibility table of Kangax

Performance

• On Layout & Web Performance
• String vs Array Concat
• Try/Catch Cost In a Loop
• Bang Function
• JQuery Find vs Context, Selector
• InnerHTML vs textContent for script text
• Long String Concatenation

• Loading...

Resources

Read This

• Annotated ECMAScript 5.1
• JavaScript Style Guide

Other Specifications

• Google JavaScript Style Guide
• JQuery Core Style Guidelines
• Principles of Writing Consistent, Idiomatic JavaScript

Other styles

• Naming this in nested functions-Christian Johansen
• Conditional Callbacks

Read more

• Understanding JavaScript Closures-Angus Croll

Books

• JavaScript: The Good Parts-Douglas Crockford
• JavaScript Patterns-Stoyan Stefanov
• Pro JavaScript Design Patterns-Ross Harmes and Dustin Diaz
• High Performance Web Sites: Essential Knowledge for Front-End Engineers-Steve Souders
• Maintainable JavaScript-Nicholas C. Zakas
• JavaScript Web Applications-Alex MacCaw
• Pro JavaScript Techniques-John Resig
• Smashing Node. js: JavaScript Everywhere-Guillermo Rauch