Large-scale Javascript

Joel Kemp

Bēhance/Adobe

@mrjoelkemp

Some of the Problems

with JAvascript at scale

Spaghetti (unstructured) Code
Too many script tags hurt performance
Language malleability creates style differences
Tooling to solve the above problems
The “send your kid off to school” problem
JS on the server

Spaghetti code

1. No clear separation of JavaScript from HTML and/or your scripting language (Python, PHP, etc).

 <div class='button' id='fansMoreBtn' onclick='loadMoreFans()'>MORE</div>

2. No clear idea of which code does what, why, and where

var visible = Number({visible});
var inviteStr = "{inviteStr}";  
var srcId= "{srcId}"; 
if (window.location.search.indexOf("v=1") > 0 ) {
  visible = 0;
}

var userFirstName = '{ui_facebookFirstName}';
var userLastName = '{ui_facebookLastName}';
var userFacebookId = '{ui_facebookId}';

Javascript MVC frameworks/libraries

Backbone.js

Angular.js

Ember.js

Why use them?

Add structure by forcing you to model your app their way

Makes application front-end architecture predictable

Community-driven solutions to common web-app problems

Zodiac Example in Backbone.js

var UserModel = Backbone.Model.extend({   defaults: {    birthday: '',    age: 0,    sign: ''  },  initialize: function () {    // Determines the age from the birthday and sets the age for this user    this.computeAge();    this.computeZodiacSign();  },  computeZodiacSign: function () {    // Simplified logic    if (this.getMonth() === 'March' && this.getDay() >= 21 ||         this.getMonth() === 'April' && this.getDay() <= 20) {      this.set('sign', 'Aries');    }  }});

ZODIAC EXAMPLE IN BACKBONE.JS

var UserView = Backbone.View.extend({  tagName: 'div',  className: 'user',   template: _.template($('#user-template').html()),   render: function () {     this.$el.html(this.template(this.model.toJSON()));   }});

The HTML Template

<script id="user-template" type="text/template">  <span>Your birthday is <%= birthday %></span><br />  <span>You are a <%= sign %></span><br />  <span>You are <%= age %> years old</span><br />  <span><%= fortune %></span><br /></script>

ZODIAC EXAMPLE IN BACKBONE.JS

var AppView = Backbone.View.extend({  el: 'app',  events: {    'click button.submit': 'handleSubmit'  },  handleSubmit: function () {    // Grab the birthday from the input fields    // Initialize a new User Model    // Create a User View whose model is the new model    // Render the view    // Add the rendered view's html somewhere  }});

Too many script tags hurt performance

Every (synchronous) script tag blocks the DOM from rendering and/or page interactivity
Users see a white screen (DOM render blocked)

depending on where the script tags are placed

Users can't scroll/interact with the page

window.load blocked

Every script tag incurs an http request's delay

A typical page

Blocks the DOM from rendering

<html>  <head>    <script src="js/jquery.min.js"></script>
    <script src="js/underscore.min.js"></script>    <script src="js/backbone.min.js"></script>
    <script src="js/UserModel.js"></script>
    <script src="js/UserView.js"></script>
    <script src="js/AppView.js"></script>    <!-- All of your other plugins/scripts -->  </head>  <body>  </body></html>

Bundle all javascript into a single file

Concatenate all used JS files into one generated JS file

Don't do this manually, there are tools as we'll see

No additional http request delay
At most a single script tag (in the ideal case)
Put the script tag at the end of the <body> tag

That file will still be large though, which could impact mobile users of your application.

Solution: Minify the bundle

Minified example

Snippet of Backbone.js' minified source code

(function(t,e){if(typeof define==="function"&&define.amd){define(["underscore","jquery","exports"],function(i,r,s){t.Backbone=e(t,s,i,r)})}else if(typeof exports!=="undefined"){var i=require("underscore");e(t,exports,i)}else{t.Backbone=e(t,{},t._,t.jQuery||t.Zepto||t.ender||t.$)}})(this,function(t,e,i,r){var s=t.Backbone;var n=[];var a=n.push;var o=n.slice;var h=n.splice;e.VERSION="1.1.2";e.$=r;e.noConflict=function(){t.Backbone=s;return this};e.emulateHTTP=false;e.emulateJSON=false;var u=e.Events={on:function(t,e,i){if(!c(this,"on",t,[e,i])||!e)return this;this._events||(this._events={});var r=this._events[t]||(this._events[t]=[]);r.push({callback:e,context:i,ctx:i||this});return this},once:function(t,e,r){if(!c(this,"once",t,[e,r])||!e)return this;var s=this;var n=i.once(function(){s.off(t,n);e.apply(this,arguments)});n._callback=e;return this.on(t,n,r)},off:function(t,e,r){var s,n,a,o,h,u,l,f;if(!this._events||!c(this,"off",t,[e,r]))return this;if(!t&&!e&&!r){this._events=void 0;return this}o=t?

Resolving File Dependencies

AppView depended on UserModel and UserView existing

Otherwise, it couldn't create instances of them

How did we guarantee that everything existed at the right time?

We organized the script tags a certain way

This doesn't scale.

Solution: AMD or CommonJS module formats to automatically deduce the order dependencies

AMD

Define a Module

define(['Backbone'], function (Backbone) {  return Backbone.Model.extend({    // Same implementation as before  });});

Require (import) a Module

define(['./UserModel', './UserView'], function (UserModel, UserView) {  var user = new UserModel();  ...})

Commonjs

Defining a module

var Backbone = require('Backbone');
module.exports = Backbone.Model.extend({  // Same stuff});

Requiring a module

var UserModel = require('./UserModel'),    UserView = require('./UserView');
var user = new UserModel();

Malleability influences style differences

See http://sideeffect.kr/popularconvention#javascript

Comma first vs Comma last

Spaces vs Tabs

Extra spaces before arguments, keywords

Single Var vs Multi-Var

Cuddled Braces vs No Cuddling

Single Quotes vs Double Quotes

...

Keeping the style the same

Style Guides

Airbnb, Google, Crockford, and more

JSHint

Enforce the same subset of the language

No double equals
No unused variables
No with statements
Only Single quotes

JSCS

Single space after keywords
Single var

Tools to automate this stuff

Grunt, Gulp, and Broccoli

Configuration based tools that let you set up your build environment
You say which tasks to execute at what time

When a .js file changes in this directory, re-concatenate all javascripts into a single file
When a concatenated bundle changes, minify that bundle
When a .js file changes, run JSHint and JSCS on it
Resolve the use of the module system (r.js or browserify)

Sample Gruntfile

 module.exports = function(grunt) {
  grunt.initConfig({
    pkg: grunt.file.readJSON('package.json'),
    concat: {
      dist: {
        src: ['src/**/*.js'],
        dest: 'dist/<%= pkg.name %>.js'
      }
    },
    uglify: {
      dist: {
        files: {
          'dist/<%= pkg.name %>.min.js': ['<%= concat.dist.dest %>']
        }
      }
    },    jshint: {
      files: ['Gruntfile.js', 'src/**/*.js', 'test/**/*.js']
    },
    watch: {
      files: ['<%= jshint.files %>'],
      tasks: ['jshint']
    }
  });};

Sample gulp-file

 var gulp = require('gulp')
    , uglify = require('gulp-uglify')
    , minifyHTML = require('gulp-minify-html')
    , sass = require('gulp-sass');gulp.task('build', function(){
    var dist = 'dist/', dirPublic = 'public/'
        , distStylesheets = dist + dirPublic + 'stylesheets/'
        , distJavascripts = dist + dirPublic + 'javascripts/';        gulp.src('public/stylesheets/scss/*.scss')
        .pipe(sass())
        .pipe(gulp.dest(distStylesheets));
    gulp.src('*.html')
        .pipe(minifyHTML())
        .pipe(gulp.dest(dist))    gulp.src('public/javascripts/*.js')
        .pipe(uglify())
        .pipe(gulp.dest(distJavascripts))
});gulp.task('default', function() {
    gulp.watch([
        'public/stylesheets/scss/**', 'public/javascripts/*.js', '*.html', '!dist/**'
    ], function(event) {
        gulp.run('build');
    });
});

Send your kids off to school

You created this javascript

Sent it off to a user's browser

And you have no idea the trouble it's causing

It could throw errors that you'll never see
It could use JS features that don't exist in that browser (IE8)
It could be ill-performant on certain platforms
It could never run (JavaScript turned off)

Javascript error logging

Muscula

Qbaka

https://gist.github.com/cheeaun/5835757

Catches errors thrown in the browser and reports them

Keeps track of error stats:

the browser used
geographic region
frequency count
time/date

JS on the server

Node.js allows JavaScript to be run on the server

To do what Python, PHP, and Java have been doing

Implement web servers
Implement (server-side) application code
Interact with the database and other services
Interact with the filesystem and OS
and more...

Can we reuse some of the code we've written already?

We've written tons of browser-centric JavaScript.

Can we reuse any of that code (those libraries)?

Isomorphic JavaScript

A unified JavaScript application across the stack
Same tools
Same language
Reusable logic
New constraints on old problems

scaling Node servers
Cross-site AJAX requests

Problems I didn't have time for

Cross-site Requests (AJAX vs CORS)

Client-side vs Server-side rendered JS apps

The future of JS: Ecmascript 6

Package Management (Bower and NPM)

RequireJS and Browserify

JavaScript Templating Engines

JS Pub/Sub Architectures vs Mediators

JS Source Maps

Pro JS Debugging with Dev Tools

Taming Async code with Promises

Reliable Functionality with Testing

Leveling Up your Javascript

Read, Code, and Read Code

Professional JavaScript for Web Developers, Zakas
JavaScript: The Good Parts, Crockford
Eloquent JavaScript (free online)
Check out John Resig's Talks on Youtube
Codecademy's JavaScript track
JavaScript Weekly
Watch JSConf talks on Youtube

Thanks

Twitter: @mrjoelkemp
Email: mrjoelkemp@gmail.com
Website: www.mrjoelkemp.com

Large scale Javascript

By Joel Kemp

Large scale Javascript

1,159

Joel Kemp

JavaScript engineer at Bēhance.

Large-scale Javascript

Some of the Problems

with JAvascript at scale

Spaghetti code

Javascript MVC frameworks/libraries

Zodiac Example in Backbone.js

ZODIAC EXAMPLE IN BACKBONE.JS

ZODIAC EXAMPLE IN BACKBONE.JS

Too many script tags hurt performance

A typical page

Bundle all javascript into a single file

Minified example

Resolving File Dependencies

AMD

Commonjs

Malleability influences style differences

Keeping the style the same

Tools to automate this stuff

Sample Gruntfile

Sample gulp-file

Send your kids off to school

Javascript error logging

JS on the server

Can we reuse some of the code we've written already?

Problems I didn't have time for

Leveling Up your Javascript

Thanks

Large scale Javascript

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