Bemto — mixins for writing BEM-style code for Jade

Table of Contents

1. Install & Use

2. Features

   • Blocks
   • Elements
   • Modifiers
   • Changing the tag name
   • Attributes
   • Context

3. Settings

   • Adding Prefix
   • Setting for Element syntax
   • Setting for Modifier syntax

4. Using for building complex mixins

Install & Use

1. Clone bemto somewhere to your project:

   git clone git://github.com/kizu/bemto.git

2. Include it in your .jade project:

   include bemto/bemto

3. Use it:

   +b.block1
     +e.element1 Foo
     +b.block2
       +e('a')(href="#bar").element Bar
     +e.element2 Baz

   would render to something like

   <div class="block1">
     <div class="block1__element1">
       Foo
     </div>
     <div class="block2">
       <a class="block2__element" href="#bar">Bar</a>
     </div>
     <div class="block1__element2">
       Baz
     </div>
   </div>

Features

Blocks

“Block” is the main thing there. It creates the block from the first passed class and creates the context for all nested elements.

You can create block calling the b mixin with some class attached to it:

+b.foo bar

That would render as

<div class="foo">bar</div>

While the simple block's syntax, of course, is harder than the simple Jade's tags, the main point is to create the contexts for elements.

Elements

“Element” is a accessory element of the block. You can read on the concept of the elements in the bem methodology, or in the great article by Nicolas Gallagher (see the “Structured class names” part). Elements often are written using the block's name plus element's name with some separator (often __ or -) in-between.

Bemto gives a convenient way to declare the elements: just use the e mixin inside any block context:

+b.foo
  +e.bar baz

This would render like

<div class="foo">
  <div class="foo__bar">baz</div>
</div>

Modifiers

“Modifier” is a state of the block or element. It is often written with the addition of it's type and/or value after the single underscore like block_mode_foo or just block_foo. However, at the most cases, the block must contain either the original block/element's class, either the modifier class.

Bemto makes it easy to write such modifiers, 'cause you don't need now to write the same block's name twice:

+b.block_foo bar

Becomes

<div class="block block_foo">bar</div>

See? You write just .block_foo but by fact get the .block.block_foo instead!

But what if you need to have more than one modifier on one block or element? Bemto have a way to do so: add a class to your block or element starting with a modifier token:

+b.block_foo._bar._baz
  +e.element_type_lol._mode_moddy Blah

and that would render as

<div class="block block_foo block_bar block_baz">
  <div class="block__element block__element_type_lol block__element_mode_moddy">
    Blah
  </div>
</div>

Changing the tag name

By default the blocks and elements render as divs. You can change it by passing the desired tag name as an argument:

+b('span').foo bar

That would render as

<span class="foo">bar</span>

Attributes

Like any Jade tag or mixin, blocks and elements can take attributes that would go to the desired tags:

+b.foo(title="Oh, it's a title")
  +e('a').bar(href='#baz') baz

would render like

<div class="foo" title="Oh, it's a title">
  <a class="foo__bar" href="#baz">baz</a>
</div>

Automatic attributes

There are some tags like img that must have at least one attribute set. Bemto would create attributes with some predefined values for such tags. So, for images this code — +b.image(src="foo.png") would render <img alt="" class="image" src="foo.png"/> — you can see that in that case there is the added empty alt.

Also, in some cases there is a need to adjust some attributes according to other ones. For img if the alt is set, but the title is not we'd need to set it to empty, 'cause there'd be a inconsistency between browsers (IE would show the title bubble for alt). And from the other side, if there is only title set in an image, we'd need to clone it to alt. Bemto do all those things.

Context

Look at the previous example: you have there some excess code that you can throw away. It's the ('a') part — as long as you set the href attribute, the block would automagically become the link. Also, there are other tags that you can omit: li in ul or ol context, or span in any already inline context.

So, here is a bigger example:

+b('ul').list
  +b.list-item
    +e.link(href="foo")
      +e.text foo
  +b.list-item
    +e.link(href="bar")
      +e.text bar

Would render to

<ul class="list">
  <li class="list-item">
    <a class="list-item__link" href="foo">
      <span class="list-item__text">foo</span>
    </a>
  </li>
  <li class="list-item">
    <a class="list-item__link" href="bar">
      <span class="list-item__text">bar</span>
    </a>
  </li>
</ul>

For now that's all, but there would be other contexts in the future of bemto.

Settings 

There are some settings you can set for different syntaxes of BEM.

For doing so, you must set them after including the bemto like this:

- bemto_settings_prefix = ''
- bemto_settings_element = '__'
- bemto_settings_modifier = '_'

Here you can see all available settings with their default values.

Adding Prefix

If you'd like to prefix all your bemto-generated blocks, you can set the bemto_settings_prefix setting to something, so it would be added to the beginning of all your blocks. Like this:

- bemto_settings_prefix = 'b-'

+b.block
  +e.element foo

and that would then render as

<div class="b-block">
  <div class="b-block__element">
    foo
  </div>
</div>

Setting for Element syntax

If you don't like the default elements syntax with the __ delimiter, you can set using the bemto_settings_element setting:

- bemto_settings_element = '-'

+b.block
  +e.element foo

this would render to

<div class="block">
  <div class="block-element">
    foo
  </div>
</div>

Setting for Modifier syntax

If you'd like to use different modifier syntax, like the one Nicolas Gallagher mentioned in his article, you can use the bemto_settings_modifier setting:

- bemto_settings_modifier = '--'

+b.block--modifier-name.--other-modifier foo

and that would expand to

<div class="block block--modifier-name block--other-modifier">
  foo
</div>

Using for building complex mixins

This is somewhat obvious, but I must mention that the bemto blocks would be great for using as the bricks for building more complex blocks. The Jade mixins work in the way where you can translate any attributes through to the any inner blocks. So you can do this:

mixin link(url)
  +b('span').link(href=url)&attributes(attributes)
    block

And then use it in this way:

+link('#Foo') Foo

+link('https://github.com')._external Github

+link('http://kizu.ru').url(rel="me") Here I am

+link Ah, I'm not a link

+link('https://github.com')
  +e.icon(src="http://favicon.yandex.net/favicon/github.com")
  +e.text Github

And that would render to

<a class="link" href="#Foo">Foo</a>

<a class="link link_external" href="https://github.com">Github</a>

<a class="link url" href="http://kizu.ru" rel="me">Here I am</a>

<span class="link">Ah, I'm not a link</span>

<a class="link" href="https://github.com">
  <img alt="" class="link__icon" src="http://favicon.yandex.net/favicon/github.com"/>
  <span class="link__text">Github</span>
</a>

There you can see almost all of the bemto features that can be used for any mixin with attributes variable attached to any inner bemto block inside of it.

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To be continued!

Id you'd like to follow on the bemto progress, follow me on twitter.

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Copyright (c) 2012 Roman Komarov kizu@kizu.ru

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