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Replaces references to non-optimized scripts or stylesheets into a set of HTML files (or any templates/views).

Watch out, this task is designed for Grunt 0.4 and upwards.

If you haven't used grunt before, be sure to check out the Getting Started guide, as it explains how to create a gruntfile as well as install and use grunt plugins. Once you're familiar with that process, install this plugin with this command:

npm install grunt-usemin --save-dev

usemin is exporting 2 different tasks:

• useminPrepare is preparing the configuration to transform specific construction (blocks) in the scrutinized file into a single line, targetting optimized version of the files (e.g concatenated, uglifyjs-ed ...)

• usemin which purpose is to replace blocks by the file they reference, and replace all references to assets by their revisioned version , if it is found on the disk. This target modifies the files it is working on.

Usually, useminPrepare is launched first, then the steps of the transformation flow (for example, concat, uglify, and cssmin), and then, in the end usemin is launched.

useminPrepare task is updating the grunt configuration to apply a configured transformation flow to tagged files (i.e. blocks). By default the transformation flow is composed of concat and uglifyjs for JS files, but it can be configured.

Blocks are expressed as:

<!-- build:<type>(alternate search path) <path> -->
... HTML Markup, list of script / link tags.
<!-- endbuild -->

• type: either js or css
• alternate search path: (optional) By default the input files are relative to the treated file. Alternate search path allow to change that
• path: the file path of the optimized file, the target output

An example of this in completed form can be seen below:

<!-- build:js js/app.js -->
<script src="js/app.js"></script>
<script src="js/controllers/thing-controller.js"></script>
<script src="js/models/thing-model.js"></script>
<script src="js/views/thing-view.js"></script>
<!-- endbuild -->

The transformation flow is made of sequential steps: each of the step transform the file, and useminPrepare will modify the configuration in order ifor the described steps to be correctly performed.

By default the flow is: concat -> uglifyjs. Additionnally to the flow, at the end, some postprocessors can be launched to alter further the configuration.

Let's have an example, using the default flow (we're just going to look at the steps), app for input dir, dist for output dir, and the following block:

<!-- build:js js/app.js -->
<script src="js/app.js"></script>
<script src="js/controllers/thing-controller.js"></script>
<script src="js/models/thing-model.js"></script>
<script src="js/views/thing-view.js"></script>
<!-- endbuild -->

The produced configurartion will look like:

{
  concat: {
    '.tmp/concat/js/app.js': [
      'app/js/app.js',
      'app/js/controllers/thing-controller.js',
      'app/js/models/thing-model.js',
      'app/js/views/thing-view.js'
      ]
  },
  uglifyjs: {
    'dist/js/app.js': ['.tmp/concat/js/app.js']
  }
}

Internally, the task parses your HTML markup to find each of these blocks, and initializes for you the corresponding Grunt config for the concat / uglify tasks when type=js, the concat / cssmin tasks when type=css.

One doesn't need to specify a concat/uglify/cssmin configuration anymore.

It is using only one target: html, with a list of the concerned files. For example, in your Gruntfile.js:

By default, it will consider the directory where the looked-at file is located as the 'root' filesystem. Each relative path (for example to a javascript file) will be resolved from this path. Same goes for the absolute ones. If you need to change the 'root' dir, use the root option (see bellow).

'useminPrepare': {
  html: 'index.html'
}

Type: 'string' Default: nil

Base directory where the transformed files should be output.

Type: 'string' Default: nil

The root directory from which your files will be resolved.

Type: 'object' Default: { steps: { 'js': ['concat', 'uglify'], 'css': ['concat', 'cssmin']}, post: {}}

This allow you to configure the workflow, either on a per-target basis, or for all the targets. You can change separately the steps or the post-processors (post).

For example:

• to change the js steps and post for the target html:

'useminPrepare', {
      html: 'index.html',
      options: {
        flow: {
          html: {
            steps: {'js': ['uglifyjs']},
            post: {}
          }
        }
      }
    }

• to change the js steps and post for all targets:

'useminPrepare', {
      html: 'index.html',
      options: {
        flow: {
          steps: {'js' : ['uglifyjs'] },
          post: []
        }
      }
    }

The given steps or post-processors may be given by strings (for the default steps and post-processors), or as object (for the user-defined ones).

User-defined steps and post-processors must have 2 attributes:

• name: name of the Gruntfile attribute that holds the corresponding config
• createConfig which is a 2 arguments function ( a context and the treated block)

For example of steps/post-processors, you can have a look at concat and uglifyjs in the lib/config directory of this repository.

The createConfig function is responsible for creating (or updating) the configuration associated to the current step/post-processor. It takes 2 arguments ( a context and the treated block), and returns a configuration object.

The context object represent the current context the step/post-processor is running in. As the step/post-processor is a step of a flow, it must be listed the input files and directory it must write a configuration for, potentially the already existing configuration. It must also indicate to the other steps/post-processor which files it will output in which directory. All this information is hold by the context object. Attributes:

• inDir: the directory where the input file for the step/post-processors will be
• inFiles: the list of input file to take care of
• outDir: where the files created by the step/post-processors will be
• outFiles: the files that are going to be created
• last: whether or not we're the last step of the flow
• options: options of the Grubntfile.js for this step (e.g. if the step is named foo, holds configuration of teh Gruntfile.js associated to the attribute foo)

The actual looked-at block, parsed an put in a structure.

Example: The following block

  <!-- build:js scripts/site.js -->',
  <script src="foo.js"></script>',
  <script src="bar.js"></script>',
  <script src="baz.js"></script>',
  <!-- endbuild -->'

is parsed as, and given to createConfig as:

var block = {
    type: 'js',
    dest: 'scripts/site.js',
    src: [
      'foo.js',
      'bar.js',
      'baz.js'
    ],
    raw: [
      '    <!-- build:js scripts/site.js -->',
      '    <script src="foo.js"></script>',
      '    <script src="bar.js"></script>',
      '    <script src="baz.js"></script>',
      '    <!-- endbuild -->'
    ]
  };

The usemin task has 2 actions:

• First it replaces all the blocks with a single "summary" line, pointing at a file creating by the transformation flow.
• Then it looks for references to assets (i.e. images, scripts, ...), and tries to replace them with their revved version if it can find one on disk

By default usemin will look for a map object created by grunt-filerev, located in grunt.filerev.summary. If it doesn not find it it will revert to disk lookup which is longer.

Note that using the options.revmap (see bellow), you can furnish a map object.

When usemin tries to replace referenced assets with their revved version it has to look at a collection of directories (asset search paths): for each of the directory of this collection it will look at the bellow tree, and try to find the revved version. This asset search directories collection is by default set to the location of the file that is scrutinized but can be modified (see Options bellow).

<link rel="stylesheet" href="styles/main.css">
<img src="../images/test.png">

By default usemin will look under dist/html for revved versions of:

• styles/main.css: a revved version of main.css will be looked at under the dist/html/styles directory. For example a file dist/html/styles/main.1234.css will match (although dist/html/main.1234.css won't: the path of the referenced file is important)
• ../images/test.png: it basically means that a revved version of test.png will be looked for under the dist/images directory

    <link rel="stylesheet" href="/styles/main.css">
    <img src="/images/test.png">

By default usemin will look under dist/html for revved versions of styles/main.css and images/test.png. Now let's suppose our assets are scattered in dist/assets. By changing the asset search path list to ['dist/assets'], the revved versions of the files will be looked under dist/assets (and thus, for example, dist/assets/images/test.875487.png and dist/assets/styles/main.98090.css) will be found.

Type: 'Array' Default: Single item array set to the value of the directory where the currently looked at file is.

List of directories where we should start to look for revved version of the assets referenced in the currently looked at file.

Example:

usemin: {
  html: 'build/index.html',
  options: {
    assetsDirs: ['foo/bar', 'bar']
  }
}

Type: 'Object' Default: Empty

Allows for user defined pattern to replace reference to files. For example, let's suppose that you want for some reason replace all references to 'image.png' in your Javascript files by the revved version of image.png found bellow the directory images. By specifying something along the lines of:

usemin: {
  js: '*.js',
  options: {
    assetsDirs: 'images',
    patterns: {
      js: [[/(image\.png)/, 'Replacing reference to image.png']]
    }
  }
}

So in short:

• key in pattern should match the target (e.g js key for the target js)
• Each pattern is an array of arrays. These arrays are composed of 4 items (last 2 are optionals):
  • First one if the regexp to use. The first group is the one that is supposed to represent the file reference to replace
  • Second one is a logging string
    • FIXME
    • FIXME

Type: 'String' Default: Empty

Indicate the location of a map file, as produced by grunt-rev for example. This map file is a simple JSON file, holding an object which attributes are the original file and associated value is the transformed file. For example:

{
  "foo.png": "foo.1234.png"
}

This map will be used instead of looking for file on the disk.

The main difference to be kept in mind, regarding directories and tasks, is that for useminPrepare, the directories needs to indicate the input, transient and output path needed to output the right configuration for the processors pipeline, whereas in the case of usemin it only reflects the output paths, as all the needed assets should have been output to the destination dir (either transformed or just copied)

useminPrepare is trying to prepare the right configuration for the pipeline of actions that are going to be applied on the blocks (for example concatenation and uglify-cation). As such it needs to have the input directory, temporary directories (staging) and destination directory. The files referenced in the block are either absolute or relative (/images/foo.png or ../../images/foo.png). Absolute files references are looked in a given set of search path (input), which by default is set to the directory where the html/css file examined is located (can be overriden per block, or more generally through root option). Relative files references are also looked at from location of the examined file, unless stated otherwise.

usemin target is replacing references to images, scrips, css, ... in the furnished files (html, css, ...). These references may be either absolute (i.e. /images/foo.png) or relative (i.e. image/foo.png or ../images/foo.png). When the reference is absolute a set of asset search paths should be looked at under the destination directory (for example, using the previous example, and searchpath equal to ['assets'], usemin would try to find either a revved version of the image of the image bellow the assets directory: for example dest/assets/images/foo.1223443.png). When the reference is relative, by default the referenced item is looked in the path relative to the current file location in the destination directory (e.g. with the preceding example, if the file is build/bar/index.html, then transformed index.html will be in dist/bar, and usemin will look for dist/bar/../images/foo.32323.png).

|
+- app
|   +- index.html
|   +- assets
|       +- js
|       +- foo.js
|       +- bar.js
+- dist

We want to optimize foo.js and bar.js into optimized.js, referenced using relative path. index.html should contain the following block:

    <!-- build:js assets/js/optimized.js -->
    <script src="assets/js/foo.js"></script>
    <script src="assets/js/bar.js"></script>
    <!-- endbuild -->

We want our files to be generated in the dist directory.

By using the following useminPrepare config:

{
  useminPrepare: {
    html: 'app/index.html',
    options: {
      dest: 'dist'
    }
  }
}

This will, on the fly, generate the following configuration:

{
  concat:
  {
    '.tmp/concat/assets/js/scripts.js': [ 
      'app/assets/js/app.js',
      'app/assets/js/services.js' 
    ] 
  },

  uglify:
  { 
    'dist/assets/js/scripts.js': [ '.tmp/concat/assets/js/scripts.js' ] 
  }
}

app
|
+- html
|   +- index.html
+- assets
|   +- js
|   +- foo.js
|   +- bar.js
+- dist

We want to optimize foo.js and bar.js into optimized.js, referenced using absolute path. index.html should contain the following block:

    <!-- build:js /assets/js/optimized.js -->
    <script src="/assets/js/foo.js"></script>
    <script src="/assets/js/bar.js"></script>
    <!-- endbuild -->

We want our files to be generated in the dist directory.

By using the following useminPrepare config:

{
  useminPrepare: {
    html: 'html/index.html',
    options: {
      root: 'app'
      dest: 'dist'
    }
  }
}

This will, on the fly, generate the following configuration:

{
  concat:
  {
    '.tmp/concat/assets/js/scripts.js': [ 
      'app/assets/js/app.js',
      'app/assets/js/services.js' 
    ] 
  },

  uglify:
  { 
    'dist/assets/js/scripts.js': [ '.tmp/concat/assets/js/scripts.js' ] 
  }
}

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