030 Closure

19 Jan 2013

Closure is a set of tools developed by Google and the Closure Compiler is part of it for JavaScript optimisation and minification. In this episode, we will take a simple JavaScript project about CSS colors and run it through the various features of Closure! We will also use the Closure Lint and check our code.

Download video: mp4

Sample code: Github

Similar episodes: 013 RequireJS, 021 GruntJS

##Background on Closure

  1. Closure
  2. Closure Compiler
  3. Closure Linter

##Things to learn with Closure

####closure linter

  1. download the closure linter with

    sudo easy_install http://closure-linter.googlecode.com/files/closure_linter-latest.tar.gz

  2. install Sublime Text package if you want to compile inside the text editor
  3. Run the closure linter:
    • from the command line: gjslint script.js
    • from inside Sublime Text: Tools > Lint > Run Closure Linter or Shift + Ctrl + Opt + J

####compiler options

####1. closure compiler server

  1. go to closure-compiler.appspot.com
  2. try out the various options for compilation level, formatting and even the warnings, errors, and post data
  3. externs url paramater will be needed for jQuery. add it to the top along with other comments for the Closure Compiler:

    // @externs_url http://closure-compiler.googlecode.com/svn/trunk/contrib/externs/jquery-1.8.js

####2. closure api

  1. create an html page according to the guide
  2. play around with the various options

####3. closure application

  1. download the zip files for closure-compiler and transfer the file compiler.jar to the project folder
  2. in the command line, navigate to the project with compiler.jar
  3. in the command line:
    • help java -jar compiler.jar --help
    • option with normal compilation java -jar compiler.jar --js script.js --js_output_file script.min.js
    • options with compilation level --compilation_level ADVANCED_OPTIMIZATIONS
    • option with warnings --warning_level VERBOSE
    • with externs for jquery ` –externs jquery.closure.js where the file jquery.closure.js` has the contents of jquery
    • with options to turn off the named class of warnings --jscomp_off=checkVars
    • with source maps --create_source_map script.min.js.map --source_map_format=V3 and add //@ sourceMappingURL=script.min.js.map at the end of the file script.min.js
  4. the complete command

    java -jar compiler.jar --compilation_level ADVANCED_OPTIMIZATIONS --js script.js --js_output_file script.min.js --warning_level VERBOSE --externs jquery.closure.js --jscomp_off=checkVars --create_source_map script.min.js.map --source_map_format=V3

####with gruntjs

  1. install gruntjs: npm install -g grunt
  2. grunt init:gruntfile to create grunt.js file. all answers can be No.
  3. npm install grunt-closure-compiler
  4. edit the file grunt.js to contain only the closure-compiler tak:

    ``` module.exports = function(grunt) {

    grunt.loadNpmTasks(‘grunt-closure-compiler’); grunt.initConfig({ ‘closure-compiler’: { frontend: { closurePath: ‘closure’, js: ‘script.js’, jsOutputFile: ‘script.min.js’, options: { compilation_level: ‘ADVANCED_OPTIMIZATIONS’, language_in: ‘ECMASCRIPT5_STRICT’, externs: ‘jquery.closure.js’, warning_level: ‘VERBOSE’, jscomp_off: ‘checkVars’, create_source_map: ‘script.closure.js.map’, source_map_format: ‘V3’, define: [ ‘“DEBUG=false”’, ‘“UI_DELAY=500”’ ] } } } });

    grunt.registerTask(‘default’, ‘closure-compiler’);

    };

    ```

##More Resources on Closure

##More resources on the episode project

##Build Link of this Episode

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