Skip to content
This repository

HTTPS clone URL

Subversion checkout URL

You can clone with HTTPS or Subversion.

Download ZIP
Fetching contributors…

Octocat-spinner-32-eaf2f5

Cannot retrieve contributors at this time

file 852 lines (756 sloc) 33.259 kb
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851
<!DOCTYPE HTML>
<html>
<head>
  <meta http-equiv="content-type" content="text/html;charset=UTF-8" />
  <meta http-equiv="X-UA-Compatible" content="chrome=1">
  <title>Jammit: Industrial Strength Asset Packaging for Rails</title>
  <style>
    body {
      font-size: 16px;
      line-height: 24px;
      background: #fafcff;
      color: #192535;
      font-family: Arial;
      font-family: "Palatino Linotype", "Book Antiqua", Palatino, FreeSerif, serif;
    }
    div.container {
      width: 720px;
      margin: 50px 0 50px 50px;
    }
    p, li {
      margin: 16px 0 16px 0;
      width: 550px;
    }
    a, a:visited {
      padding: 0 2px;
      text-decoration: none;
      background: #cadaea;
      color: #192535;
    }
    a:active, a:hover {
      color: #000;
      background: #bacada;
    }
    h1, h2, h3, h4, h5, h6 {
      margin-top: 40px;
    }
    b.header {
      font-size: 18px;
    }
    span.alias {
      font-size: 14px;
      font-style: italic;
      margin-left: 20px;
    }
    table {
      margin: 16px 0; padding: 0;
    }
      tr, td {
        margin: 0; padding: 0;
      }
        td {
          padding: 9px 15px 9px 0;
        }
          td.definition {
            line-height: 18px;
            font-size: 14px;
          }
    code, pre, tt {
      font-family: Monaco, Consolas, "Lucida Console", monospace;
      font-size: 12px;
      line-height: 18px;
      color: #294555;
    }
      code {
        margin-left: 20px;
      }
      pre {
        font-size: 12px;
        padding: 2px 0 2px 12px;
        border-left: 6px solid #99aabb;
        margin: 0px 0 30px;
      }
    #diagram {
      margin: 20px 0 0 0;
    }
  </style>
</head>
<body>

  <div class="container">

    <p>
      <img src="http://jashkenas.s3.amazonaws.com/images/jammit/jammit.png" alt="Jammit" />
    </p>

    <p>
      <a href="http://github.com/documentcloud/jammit/">Jammit</a> is an
      industrial strength asset packaging library for <b>Rails</b>, providing
      both the CSS and JavaScript concatenation and compression
      that you'd expect, as well as <b>YUI Compressor</b> and <b>Closure Compiler</b>
      compatibility, ahead-of-time gzipping, built-in JavaScript template
      support, and optional <b>Data-URI / MHTML image and font embedding</b>.
    </p>

    <p>
      <b>Current Version:</b> <a href="http://rubygems.org/gems/jammit/">0.6.0</a>
    </p>
    
    <p>
      You can report bugs and discuss features on the
      <a href="http://github.com/documentcloud/jammit/issues">issues page</a>,
      on Freenode in the <tt>#documentcloud</tt> channel,
      or send tweets to <a href="http://twitter.com/documentcloud">@documentcloud</a>.
    </p>

    <p>
      <i>Jammit is an open-source component of <a href="http://documentcloud.org/">DocumentCloud</a>.</i>
    </p>

    <h2>Table of Contents</h2>

    <p style="line-height: 30px;">
      <a href="#installation">Installation</a> |
      <a href="#configuration">Configuration</a> |
      <a href="#usage">Usage</a> |
      <a href="#compressors">YUI &amp; Closure</a> |
      <a href="#precaching">Precaching Assets</a> <br />
      <a href="#expires">Expires Headers</a> |
      <a href="#embedding">Embedding Assets</a> |
      <a href="#jst">JavaScript Templates</a> |
      <a href="#changes">Changes</a>
    </p>

    <h2>Links</h2>

    <p style="line-height: 30px;">
      <a href="http://github.com/documentcloud/jammit">Source Code</a> |
      <a href="http://documentcloud.github.com/jammit/doc/">Internal Docs</a> |
      <a href="http://jashkenas.s3.amazonaws.com/misc/jammit_example/normal.html">Image Embedding Example</a>
    </p>

    <h2 id="installation">Installation</h2>

    <ol>
      <li>
        Grab the gem:<br />
        <tt>gem install jammit</tt>
      </li>
      <li>
        Add the gem to Rails' <b>environment.rb</b> inside of the initializer:<br />
        <tt>config.gem "jammit"</tt>
      </li>
      <li>
        <p>
          If you're using <b>Rails 3</b>, you're done! Jammit routes
          (under <b>/assets</b> by default) will be loaded automatically into
          your app.
        </p>
        <p>
          If you're using <b>Rails 2</b>, edit <b>config/routes.rb</b> to give
          Jammit routes for dynamic asset packaging and caching.
        </p>
<pre>
ActionController::Routing::Routes.draw do |map|
  ...
  Jammit::Routes.draw(map)
  ...
end</pre>
      </li>
    </ol>

    <p>
      <i>Note: If you don't already have the
      <a href="http://github.com/sstephenson/ruby-yui-compressor">ruby-yui-compressor</a> or
      <a href="http://github.com/documentcloud/closure-compiler">closure-compiler</a>
      gems installed, downloading make take a minute &mdash; the jar files together
      weigh in at 5 megabytes.</i>
    </p>

    <h2 id="configuration">Configuration</h2>

    <p>
      Jammit uses the <b>config/assets.yml</b> YAML configuration file to define
      packages and to set extra options. A package is an ordered set of directory glob
      rules that will be expanded into a unique list of files. An example of
      a complete <b>assets.yml</b> follows:
    </p>

<pre>
embed_assets: on

javascripts:
  workspace:
    - public/javascripts/vendor/jquery.js
    - public/javascripts/lib/*.js
    - public/javascripts/views/**/*.js
    - app/views/workspace/*.jst

stylesheets:
  common:
    - public/stylesheets/reset.css
    - public/stylesheets/widgets/*.css
  workspace:
    - public/stylesheets/pages/workspace.css
  empty:
    - public/stylesheets/pages/empty.css</pre>

    <p>
      There are a number of extra configuration options that you may add to the
      <b>assets.yml</b> configuration file to customize the way Jammit behaves.
      Here's an <a href="https://gist.github.com/667693">example configuration file</a>
      using all of the possible options. The meaning of the options and their
      default values are listed below. Don't be bewildered by the length of the
      list &mdash; none of the options are required, they just give you fine-grained
      control over how your packages are generated.
    </p>

    <table>
      <tr>
        <td><b>package_assets</b></td>
        <td><tt>on&nbsp;|&nbsp;off&nbsp;|&nbsp;always</tt></td>
        <td class="definition">
          Defaults to <b>on</b>, packaging and caching assets in every environment
          but <tt>development</tt> and <tt>test</tt>.
          Never packages when <b>off</b>, always packages when <b>always</b>.
        </td>
      </tr>
      <tr>
        <td><b>embed_assets</b></td>
        <td><tt>on&nbsp;|&nbsp;off&nbsp;|&nbsp;datauri</tt></td>
        <td class="definition">
          Defaults to <b>off</b>. When <b>on</b>, packages and caches Data-URI
          and MTHML variants of your stylesheets, with whitelisted images
          embedded inline. Using <b>datauri</b> serves embedded images only
          to browsers that support Data-URIs, and serves unmodified stylesheets
          to Internet Explorer 7 or lower.
        </td>
      </tr>
      <tr>
        <td><b>compress_assets</b></td>
        <td><tt>on&nbsp;|&nbsp;off</tt></td>
        <td class="definition">
          Defaults to <b>on</b>. When <b>off</b>, JavaScript and CSS packages
          will be left uncompressed (by YUI or Closure). Disabling compression is only recommended
          if you're packaging assets in development.
        </td>
      </tr>
      <tr>
        <td><b>gzip_assets</b></td>
        <td><tt>on&nbsp;|&nbsp;off</tt></td>
        <td class="definition">
          Defaults to <b>on</b>. When <b>off</b>, only the plain version of the
          asset will be written out, not the <tt>.gz</tt> alternative. Disable this
          if you don't plan on configuring your webserver to serve the static
          gzip alternatives.
        </td>
      </tr>
      <tr>
        <td><b>javascript_compressor</b></td>
        <td><tt>yui&nbsp;|&nbsp;closure</tt></td>
        <td class="definition">
          Defaults to <b>yui</b>. As of <b>0.2.0</b>, the Jammit gem can use either the
          <a href="http://developer.yahoo.com/yui/compressor/">YUI Compressor</a>
          or the
          <a href="http://code.google.com/closure/compiler/">Google Closure Compiler</a>
          to compress your JavaScript.
        </td>
      </tr>
      <tr>
        <td><b>allow_debugging</b></td>
        <td><tt>on&nbsp;|&nbsp;off</tt></td>
        <td class="definition">
          Defaults to <b>on</b>. Leaving it on allows you to pass
          <tt>debug_assets=true</tt> as a query parameter, in order to load the
          page with uncompressed, unpackaged assets in production.
        </td>
      </tr>
      <tr>
        <td><b>template_function</b></td>
        <td><tt>on&nbsp;|&nbsp;off&nbsp;|&nbsp;...</tt></td>
        <td class="definition">
          The JavaScript function that compiles your JavaScript templates (<b>JST</b>).
          Defaults to <b>on</b>, which uses a bundled variant of
          <a href="http://ejohn.org/blog/javascript-micro-templating/">Micro-Templating</a>.
          Set it to <b>_.template</b> if you use
          <a href="http://documentcloud.github.com/underscore/">Underscore.js</a>,
          or <b>new&nbsp;Template</b> for
          <a href="http://www.prototypejs.org/">Prototype</a>. Turn it <b>off</b>
          to pass through the template strings unaltered.
        </td>
      </tr>
      <tr>
        <td><b>template_namespace</b></td>
        <td><tt>...</tt></td>
        <td class="definition">
          By default, all of your compiled templates will be added to a top-level
          <b>window.JST</b> object. If you'd like to add them instead to your
          own JavaScript namespace, change it to the
          object of your choice.
        </td>
      </tr>
      <tr>
        <td><b>template_extension</b></td>
        <td><tt>...</tt></td>
        <td class="definition">
          By default, Jammit treats files with a <tt>jst</tt> extension as
          JavaScript templates. If you'd prefer to use a different extension, like
          <tt>html.mustache</tt>, set the <b>template_extension</b> option.
        </td>
      </tr>
      <tr>
        <td><b>package_path</b></td>
        <td><tt>...</tt></td>
        <td class="definition">
          The URL at which packaged assets are cached and made available.
          Defaults to <b>assets</b>, but if you already have an existing
          AssetsController with a different purpose, you could change it to, say,
          <b>packages</b>. <i>(Single directory names only, please.)</i>
        </td>
      </tr>
      <tr>
        <td><b>compressor_options</b></td>
        <td><tt>...</tt></td>
        <td class="definition">
          Pass an options hash directly to the underlying JavaScript compressor
          to configure it. See the
          <a href="http://github.com/sstephenson/ruby-yui-compressor">ruby-yui-compressor</a> or
          <a href="http://github.com/documentcloud/closure-compiler">closure-compiler</a>
          gem documentation for the full list of available options.
        </td>
      </tr>
      <tr>
        <td><b>css_compressor_options</b></td>
        <td><tt>...</tt></td>
        <td class="definition">
          Pass an options hash directly to the YUI CSS Compressor.
          <a href="http://yui.rubyforge.org/classes/YUI/CssCompressor.html">Available options</a>
          are <b>charset</b>, and <b>line_break</b>, which can be used to write
          out each CSS rule on a separate line.
        </td>
      </tr>
    </table>

    <p>
      The contents of <tt>assets.yml</tt> are passed through <b>ERB</b> before
      being loaded, in case you find the need to configure Jammit
      for different environments.
    </p>

    <p>
      <i>Warning: In <b>Rails 3</b>, static assets are not served by default.
      You either have to configure your webserver to serve static assets out
      of</i> <tt>public</tt> <i>(recommended), or set</i>
      <tt>config.serve_static_assets = true</tt>
    </p>

    <h2 id="usage">Usage</h2>

    <p>
      To access your packages in views, use the corresponding helper. The
      helper methods can include multiple packages at once:
    </p>

    <pre>
&lt;%= include_stylesheets :common, :workspace, :media => 'all' %&gt;
&lt;%= include_javascripts :workspace %&gt;</pre>

    <p>
      In development, no packaging is performed, so you'll see a list of individual
      references to all of the JavaScript and CSS files. The <b>assets.yml</b>
      configuration file is reloaded on every development request, so you can
      change the contents of your packages without needing to restart Rails.
      In all other environments, or if <b>package_assets</b> is set to "<b>always</b>",
      you'll get tags for the merged packages.
    </p>
    
    <p>
      If <b>allow_debugging</b> is left on, you'll be able to request the development
      version of the assets for any given page, by passing <tt>debug_assets=true</tt>
      as a query parameter.
    </p>

    <p>
      You can easily use Jammit within your Rakefile, and other scripts:
    </p>

    <pre>require 'jammit'
Jammit.package!</pre>

    <h2 id="compressors">YUI &amp; Closure</h2>

    <p>
      Jammit can be configured to use either the
      <a href="http://developer.yahoo.com/yui/compressor/">YUI Compressor</a> or the
      <a href="http://code.google.com/closure/compiler/">Google Closure Compiler</a>
      to compress and optimize your JavaScript. (CSS is always run through the
      YUI Compressor.) Specify the <b>javascript_compressor</b> to choose either <b>yui</b>
      or <b>closure</b> backends. If left blank, Jammit defaults to <b>yui</b>.
    </p>

    <p>
      You can configure the JavaScript compilation by adding <b>compressor_options</b>
      to your <b>assets.yml</b>. The <b>compressor_options</b>
      will be passed directly to the Gem backend of your chosen compressor. See the
      <a href="http://github.com/sstephenson/ruby-yui-compressor">ruby-yui-compressor</a> or
      <a href="http://github.com/documentcloud/closure-compiler">closure-compiler</a>
      gem documentation for all the available options. For example, to configure
      the Closure Compiler to use its
      <a href="http://code.google.com/closure/compiler/docs/compilation_levels.html">advanced optimizations</a>,
      you would add the <b>compilation_level</b>:
    </p>

<pre>
javascript_compressor: closure
compressor_options:
  compilation_level: "ADVANCED_OPTIMIZATIONS"
</pre>

    <p>
      Jammit always uses the YUI CSS Compressor to compress CSS files. You can
      <a href="http://yui.rubyforge.org/classes/YUI/CssCompressor.html">configure it</a>
      by specifying the <b>css_compressor_options</b>, in <b>assets.yml</b>.
    </p>

    <p>
      <i>
        <b>Warning:</b> Google's Closure Compiler has been known to choke on certain
        already pre-compressed JavaScripts, such as the production version of jQuery.
        Using the uncompressed development version is recommended.
      </i>
    </p>

    <h2 id="precaching">Precaching Assets</h2>

    <p>
      Installing the Jammit gem provides the optional but handy <tt>jammit</tt> command-line utility,
      which can be hooked into your deployment process. The <tt>jammit</tt>
      command reads in your configuration file, generates all of the defined
      packages, and gzips them at the highest compression setting. In order to
      serve these static gzipped versions, configure your <b>Nginx</b>
      <a href="http://wiki.nginx.org/NginxHttpGzipStaticModule">http_gzip_static_module</a>,
      or your <b>Apache</b>
      <a href="http://httpd.apache.org/docs/2.0/content-negotiation.html">Content Negotiation MultiViews</a>.
      It's also a good idea to have gzip compression turned on for the remainder
      of your static assets, including any asset packages that aren't gzipped-in-advance.
      Adding <b>Nginx</b>'s
      <a href="http://wiki.nginx.org/NginxHttpGzipModule">http_gzip_module</a>
      or <b>Apache</b>'s
      <a href="http://httpd.apache.org/docs/2.0/mod/mod_deflate.html">mod_deflate</a>
      will do the trick.
    </p>

    <p>
      The <tt>jammit</tt> command can be passed options to configure the
      path to <b>assets.yml</b>, and the output directory in which all packages
      are compiled. Run <tt>jammit --help</tt> to see all of the options. For
      speedy builds, <tt>jammit</tt> will check the modification times of your packages
      and source files: only the packages that have changed are rebuilt. If you'd
      like to force all packages to build, use <tt>jammit --force</tt>.
    </p>

    <p>
      In production, you'll want to run Jammit during deployment, somewhere
      in between updating the source and symlinking to the new release. Whether you're
      using <a href="http://www.capify.org/index.php/Capistrano">Capistrano</a>,
      <a href="http://rubyhitsquad.com/Vlad_the_Deployer.html">Vlad</a>,
      or just good 'ol <a href="http://rake.rubyforge.org/">Rake</a>,
      it shouldn't be too hard to add a step that calls the <tt>jammit</tt> command.
      For an example Jammit setup under Capistrano and Apache, see
      <a href="http://afreshcup.com/home/2010/1/18/notes-on-using-jammit-with-rails.html">Mike Gunderloy's blog post</a>.
    </p>

    <h2 id="expires">Expires Headers</h2>

    <p>
      To get the fastest page load times for your regular visitors, it's recommended
      to set the HTTP Expires header to a date far in the future. You don't need
      to worry about clearing the cached assets when you deploy a new release,
      because Rails will write out the asset's modification time as part of the URL,
      causing browsers to fetch a fresh copy of the asset.
    </p>

    <p>
      If you're using an <b>Nginx</b> webserver, add the following snippet to the
      <br /><tt>server { ... }</tt> block for your application:
    </p>

    <pre>
location ~ ^/assets/ {
  passenger_enabled on;
  expires max;
}</pre>

    <p>
      If you're using <b>Apache</b>, make sure that
      <a href="http://httpd.apache.org/docs/1.3/mod/mod_expires.html">mod_expires</a>
      is enabled, and then add the following snippet to the
      appropriate <b>VirtualHost</b> section of your configuration,
      filling in the path to your deployed application:
    </p>

    <pre>
ExpiresActive On
&lt;Directory "/path/to/public/assets"&gt;
  ExpiresDefault "access plus 1 year"
&lt;/Directory&gt;</pre>

    <p>
      If for any reason (multiple physical servers, rsync-only deploys) you don't
      wish to rely on modification times for cache expiry, Jammit uses the
      standard Rails helpers to generate URLs, and will respect
      the <tt>RAILS_ASSET_ID</tt> environment variable.
    </p>

    <h2 id="embedding">Embedding Images ...</h2>

    <p>
      After you've finished concatenating and compressing your JavaScript and
      CSS files into streamlined downloads, the slowest part of your page load
      is probably the images. It's common to use image sprites to avoid the
      avalanche of HTTP requests that are needed to load a bunch of small images.
      Unfortunately, image sprites can be complicated to position (especially
      with horizontal and vertical tiling), and a real pain to create and
      maintain. With a little elbow grease from Jammit, your spriting woes can be a
      thing of the past.
    </p>

    <p>
      With <b>embed_assets</b> turned on, Jammit will inline image files directly
      into your compiled CSS, using
      <a href="http://en.wikipedia.org/wiki/Data_URI_scheme">Data-URIs</a> in
      supported browsers, and
      <a href="http://en.wikipedia.org/wiki/Mhtml">MHTML</a> in Internet Explorer 7 and below.
      Instead of ten CSS files referencing 30 images, you can have a single,
      packaged, minified, gzipped CSS file, with the images coming in all at
      once instead of piecemeal, making just a single HTTP request.
    </p>

    <p>
      Take a look at this example (especially on a slow connection or wifi):<br />
      <a href="http://jashkenas.s3.amazonaws.com/misc/jammit_example/normal.html">Normal Image Loading</a> vs.
      <a href="http://jashkenas.s3.amazonaws.com/misc/jammit_example/jammit.html">Jammit Image Embedding</a><br />
    </p>

    <p>
      Embedded images can be a little tricky, which is why using them is strictly
      on an opt-in basis. After enabling <b>embed_assets</b> in the configuration file,
      you'll need to whitelist the images that you'd like to make embeddable.
      When processing CSS, Jammit will only embed images that have
      <b>.../embed/...</b> somewhere in their path &mdash; the other images will be
      left untouched. You can make a single <b>public/images/embed</b> folder for
      your embedded images, or organize them into directories however you
      prefer. It's not recommended to embed all of your site's images, just
      the ones that conform to the following three rules:
    </p>

    <ol>
      <li>
        <b>Images that are small.</b> Large images will simply delay the rendering
        of your CSS. Jammit won't embed images larger than <b>32 kilobytes</b>, because
        Internet Explorer 8 won't render them.
      </li>
      <li>
        <b>Images that are immediately visible.</b> It's better to leave the
        images that are hidden at page load time to download in the background.
      </li>
      <li>
        <b>Images that are referenced by a single CSS rule.</b> Referencing the
        same embedded image in multiple rules will cause that image's contents to be
        embedded more than once, defeating the purpose. Replace the duplicated
        rules with an image-specific HTML class, and you're good to go.
      </li>
    </ol>

    <p>
      A final <b>cautionary note</b>. Internet Explorer's implementation of MHTML
      requires the use of absolute paths in image references. This means that
      the timestamp that Rails appends to the stylesheet URL (to allow
      far-future expires headers) needs to also be in the contents of the
      stylesheet. If a process on your webserver changes the modification time
      of the cached MHTML stylesheet, it will break the image references. To fix
      it, use the <tt>jammit</tt> command (with <tt>--base-url</tt>) to rebuild your assets, or simply delete
      the cached file, and let Jammit automatically rebuild the file on the next
      request.
    </p>

    <p>
      If the MHTML stylesheets sound too fragile, or if you encounter any problems
      with them in Internet Explorer (such as mixed-mode warnings when serving
      MHTML through SSL), we recommend setting <b>embed_assets</b> to "<b>datauri</b>".
      Using "<b>datauri</b>" will cause Internet Explorer 7 and below to receive
      plain versions of the packaged stylesheets, while all other browsers get the
      Data-URI flavor.
    </p>

    <h3>... and Embedding Fonts</h3>

    <p>
      Embedded fonts work in largely the same way as images, <b>TTF</b> and <b>OTF</b> files
      that are whitelisted within an "embed" folder will be inlined as Data-URIs.
      There is no MHTML variant for fonts, because Internet Explorer only supports
      unembeddable <b>EOT</b> files. Embedding is especially important
      for fonts in general, because it helps avoid
      <a href="http://paulirish.com/2009/fighting-the-font-face-fout/">the flash of unstyled text</a>
      that the browser would otherwise display while waiting for the font to
      download. If you're looking to get started with web fonts,
      <a href="http://www.fontsquirrel.com/fontface/generator">FontSquirrel has a great tool</a>
      that can generate the proper fonts and styles you'll need. Here's an example
      of a CSS rule that would activate the proper Jammit embedding:
    </p>

<pre>
@font-face {
  font-family: 'DroidSans';
  src: url(/fonts/DroidSans.eot);
  src: local('Droid Sans'), local('DroidSans'), url(/fonts/embed/DroidSans.ttf) format('truetype');
}</pre>

    <h2 id="jst">JavaScript Templates</h2>

    <p>
      If you're using enough JavaScript to want it compressed and concatenated,
      you're probably using it to generate at least a little of your
      HTML. Traditionally, this has been accomplished by joining together strings
      and inserting them into the DOM. A far more agreeable way to generate HTML
      on the client is to use JavaScript templates (referred to here as <b>JST</b>).
    </p>

    <p>
      Jammit helps keep your JavaScript views organized alongside your Rails
      views, bundling them together into packages, and providing them pre-compiled
      for your client-side code to evaluate. If left unspecified, Jammit uses a variant of
      <a href="http://ejohn.org/blog/javascript-micro-templating/">John Resig's Micro Templating</a>
      to compile the templates, but you can choose your preferred JavaScript templating engine
      of your choosing by setting the <b>template_function</b> in <b>assets.yml</b>.
      Jammit will run all of your templates through the function, and assign
      each one by filename to a top-level <b>JST</b> object. For example, the following
      template, <b>app/views/drivers/license.jst</b>:
    </p>

<pre>
&lt;div class="drivers-license"&gt;
  &lt;h2&gt;Name: &lt;%= name %&gt;&lt;/h2&gt;
  &lt;em&gt;Hometown: &lt;%= birthplace %&gt;&lt;/em&gt;
  &lt;div class="biography"&gt;
    &lt;%= bio %&gt;
  &lt;/div&gt;
&lt;/div&gt;</pre>

    <p>
      Including this template within a JavaScript asset package makes it
      available within the browser as the <b>JST.license</b> function.
    </p>

<pre>
JST.license({name : "Moe", birthplace : "Brooklyn", bio : "Moe was always..."});</pre>
    
    <p>
      Since <b>0.5.0</b>, templates should be included in the appropriate
      <tt>javascripts</tt> package. Here's an example of an <tt>assets.yml</tt>
      that uses templates, and shows the location at which they'll be available
      on the client. When including templates from different directories, the
      common prefix is ignored, and the rest of the path becomes the name of the
      template:
    </p>

<pre>
javascripts:
  workspace:
    - app/views/accounts/badge.jst
    - app/views/common/dialog.jst
    - app/views/common/menu.jst</pre>

    <p>
      Then, from your JavaScript:
    </p>

<pre>
JST['accounts/badge']
JST['common/dialog']
JST['common/menu']</pre>

    <p>
      To use <a href="http://documentcloud.github.com/underscore/">Underscore.js</a>
      templates, set <b>template_function</b> to <tt>_.template</tt>.<br />
      To use <a href="http://www.prototypejs.org/">Prototype</a> templates, set
      it to <tt>new Template</tt>.<br />To use
      <a href="http://github.com/janl/mustache.js">Mustache.js</a> templates,
      you'll need
      <a href="http://gist.github.com/234982">a little extra setup</a>.<br />
      If you'd rather leave your template strings as strings, and compile them later,
      set <b>template_function</b> to <tt>off</tt>.
    </p>

    <p>
      The default extension for template files is <tt>jst</tt>,
      but you can set <b>template_extension</b> in your <tt>assets.yml</tt> if you're
      using an engine with a preferred extension, such as <tt>html.mustache</tt>
    </p>

    <h2 id="changes">Change Log</h2>
    
    <p>
      <b class="header">0.6.0</b><br />
      You can now pass <tt>debug_assets=true</tt> as a query parameter to debug
      the un-packaged versions of your assets in production ... and disable this
      feature by specifying <tt>allow_debugging: off</tt>.
      Fixes for relative URL rewriting when Regex-unsafe characters exist in the
      base path.
      Fixes binary-mode file reading for some versions of Ruby 1.8 on Windows.
      It's now possible to embed <tt>.woff</tt>-formatted fonts in stylesheets,
      along with the rest.
    </p>

    <p>
      <b class="header">0.5.4</b><br />
      Added a <tt>Jammit.package!</tt> helper function, for use in Rake tasks.
      Fixed a <tt>request_uri</tt> deprecation warning for Rails 3.
      Bugfix to allow <tt>template_extension</tt> to include periods.
    </p>

    <p>
      <b class="header">0.5.3</b><br />
      You can now embed <b>WOFF</b>-formatted fonts.
      Jammit warnings avoid use of <tt>Rails.logger</tt>.
      Bugfixes for Ruby 1.9.2 with asset files containing Unicode characters.
    </p>

    <p>
      <b class="header">0.5.1</b><br />
      Included missing <tt>rails/routes.rb</tt> file in the Gem manifest for Rails 3.
    </p>

    <p>
      <b class="header">0.5.0</b><br />
      The Jammit gem is now compatible with Rails 3. JST template packages are
      no longer specified separately. This is a backwards-incompatible change,
      and you'll have to update your <tt>assets.yml</tt> file to simply include
      the JST in your existing JavaScript packages, as shown above. Alongside
      this change, template names are now better namespaced &mdash; see the
      section on <b>JavaScript Templates</b> for the details.
      Bugfix for IE8 and Data-URIs slightly under 32kb in size, as well as
      for MHTML in IE7-mode in Vista.
    </p>

    <p>
      <b class="header">0.4.4</b><br />
      Jammit will now add the <tt>RAILS_ASSET_ID</tt> timestamp to image URLs
      within your CSS packages, if configured, for better cache-busting.
      <a href="http://github.com/ghazel/">Greg Hazel</a> contributed a series
      of Jammit/Windows bug fixes.
    </p>

    <p>
      <b class="header">0.4.3</b><br />
      Bugfix for building on Windows with drive-letter absolute paths.
    </p>

    <p>
      <b class="header">0.4.2</b><br />
      Added a logged warning when you have rules in <b>assets.yml</b> that don't
      match any files.
    </p>

    <p>
      <b class="header">0.4.1</b><br />
      Jammit is now able to embed <tt>@font-face</tt> web fonts in <b>TTF</b> and
      <b>OTF</b> formats. The <b>embed_images</b> option has been renamed to
      <b>embed_assets</b> for this change. The <b>assets.yml</b> file is now
      passed through ERB before being loaded, so you can configure
      environment-specific settings, just like you would with <b>database.yml</b>.
    </p>

    <p>
      <b class="header">0.3.3</b><br />
      Added <tt>css_compressor_options</tt> to assets.yml, so you can
      set <tt>charset</tt> and <tt>line_break</tt> for the YUI CSS Compressor.
    </p>

    <p>
      <b class="header">0.3.2</b><br />
      If Java isn't available on your machine, Jammit will now run in a graceful
      degraded mode, where assets are packaged but not compressed. You can now
      pass <tt>:embed_assets => false</tt> to the <tt>include_stylesheets</tt>
      helper to disable image embedding on a per-package basis.
    </p>

    <p>
      <b class="header">0.2.8</b><br />
      Jammit now correctly rewrites relative image URLs within CSS, for easier
      integration with partial Rails apps deployed on sub-paths.
    </p>

    <p>
      <b class="header">0.2.7</b><br />
      The <tt>jammit</tt> command has been enhanced to check the modification times of
      your packages &mdash; if no source files have changed, the package isn't
      rebuilt.
    </p>

    <p>
      <b class="header">0.2.6</b><br />
      Jammit now raises an exception if Java isn't installed, or if the Java
      version is unsupported by your JavaScript compressor of choice.
    </p>

    <p>
      <b class="header">0.2.5</b><br />
      When specifying your asset packages as directory globs, absolute globs are
      now absolute, and relative globs are relative to RAILS_ROOT.
    </p>

    <p>
      <b class="header">0.2.4</b><br />
      Jammit now throws a <tt>ConfigurationNotFound</tt> error when attempting to load
      a nonexistent configuration file. Resolved an issue with asset caching from
      daemonized mongrels.
    </p>

    <p>
      <b class="header">0.2.1</b><br />
      The <tt>include_stylesheets</tt> helper now takes the same options as the
      Rails <tt>stylesheet_link_tag</tt> helper (such as <tt>:media => 'print'</tt>).
    </p>

    <p>
      <b class="header">0.2.0</b><br />
      Jammit now supports the <b>Google Closure Compiler</b> as an alternative
      to the YUI compressor.
    </p>

    <p>
      <b class="header">0.1.3</b><br />
      Fixed a bug that conflicted with other plugins trying to alter
      ApplicationController in development.
    </p>

    <p>
      <b class="header">0.1.1</b><br />
      Added support for embedding images with stylesheet-relative paths.
      Shortened the MHTML identifiers.
    </p>

    <p>
      <b class="header">0.1.0</b><br />
      Initial Jammit release.
    </p>

    <p>
      <br />
      <a href="http://documentcloud.org/" title="A DocumentCloud Project" style="background:none;">
        <img src="http://jashkenas.s3.amazonaws.com/images/a_documentcloud_project.png" alt="A DocumentCloud Project" style="position:relative;left:-10px;" />
      </a>
    </p>

    </div>

  </div>

</body>
</html>
Something went wrong with that request. Please try again.