bemto

by kizu

kizu /bemto

Smart mixins for writing BEM in Pug

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Bemto — mixins for writing BEM-style code for Pug Build Status NPM version

Table of Contents

  1. Install & Use
  2. Features

  3. Settings

  4. Using for building complex mixins

Install & Use

Cloning

  1. Clone

    bemto
    somewhere to your project:
    git clone git://github.com/kizu/bemto.git
    
  2. Include it in your

    .pug
    project:
    include bemto/bemto.pug
    
  3. Use it:

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

    would render to something like

    Foo
    Bar
    Baz

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

bar

While the simple block's syntax, of course, is harder than the simple Pug'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

baz

Context of the element

Note that bemto uses the first classname of the block as a context for further elements. If you'd like to use another class without changing the order, you can mark it with

__
in the end:
+b.foo.bar__
  +e.baz

This way instead of

foo
bemto would base the nested elements from the
bar
:

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

bar

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

Blah

You can also use shorter modifier syntax like

class="block -modifier"
(but only when this syntax won't be used for delimiting full modifiers or elements).
+b.-foo.-bar.-baz

this would render to

Changing the tag name

By default the blocks and elements render as

div
s. You can change it by passing the desired tag name as the first class in uppercase:
+b.SPAN.foo bar

Or by passing an

options
object with a
tag
param:
+b({tag: 'span'})foo bar

Either way would render as

bar

Attributes

Like any Pug 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

baz

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
— 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



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

Redefining tag's metadata

In a case you'd like some tag to set a different context, i.e. to override it's content_type, you can use a

metadata
option for the block/element. For example, if you'd like a link to have block context, you can redefine it in this way:
+b({ metadata: { content_type: 'block' } }).A.foo
  +e.bar

would render as


baz

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:
-
  set_bemto_settings({
    prefix: '',
    element: '__',
    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

prefix
setting to a String or an Object.

Strings for prefix setting

If you'd set a string, it would be just prepended to the names of all blocks:

- set_bemto_settings({ prefix: 'b-' })

+b.block +e.element foo

and that would then render as

foo

Note that if you had already used this prefix in a classname, it won't be added, so you won't have occasional duplicated prefixes.

Objects for prefix setting

If you'd want to have more control over prefixes, you can use a special object instead of a string:

-
  set_bemto_settings({
    prefix: {
      '': 'b-',
      'js-': true,
      'is-': 'is-',
      'global-': '',
      'nope-': false,
      'sc-': 'shortcut-'
    }
  })

Look at the above example, it have all the variations the prefix object accepts:

  • The empty string for key works the same as a string setting: you'd get the value for this key prepended for all classnames without detected prefixes.

  • If a value for any key is

    true
    , this prefix would be always treated as such and won't be prepended by other prefixes.
  • If a value for a key is

    false
    or an empty string, the classnames with this prefix would be rendered without it.
  • In other cases, where the key and the value are both strings, all the key prefixes in the source code would be replaced with the value ones, and also all of those prefixes would be treated as registered ones, so you wouldn't add other prefixes for them.

Setting for Element syntax

If you don't like the default elements syntax with the

__
delimiter, you can set using the
element
setting:
- set_bemto_settings({ element: '-' })

+b.block +e.element foo

this would render to

foo

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

modifier
setting:
- set_bemto_settings({ modifier: '--' })

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

and that would expand to

foo

Setting for allowing nested elements

There can be cases when you could want to make elements of elements, i.e. when using element names instead of block names:

+b.block-element
  +e.element2

renders by default to

If you'd like to have

foo__bar__baz
in the output instead, you can set the
flat_elements
to
false
:
- set_bemto_settings({ flat_elements: false })

+b.foo__bar +e.baz

This would render with the nested element:

Scope for the settings

If you'll need to have some settings just in a certain scope, you can wrap your code in

bemto_scope
mixin, passing your desired settings right into it:
+b.foo_bar
  +bemto_scope({
      prefix: 'b-',
      element: '-',
      modifier: '--'
    })
    +b.nnnn
      +e.mmmm--kkkk
  +e.baz

Would render as

Setting for the output syntax of the elements/modifiers

If you'd like to use different syntax of the element/modifier delimiter in Pug source and the html output, you can use the

ouput_element
and
output_modifier
settings, otherwise the same delimiter as in the
element
and
modifier
settings would be used.
-
  set_bemto_settings({
    element: '-',
    modifier: '--',
    output_element: '__',
    output_modifier: '_'
  })

+b.block.block2- +e.element--modifier foo

would output

foo

You can see how the source uses the

-
for element and
--
for modifier, but the result gets
__
and
_
instead.

Setting for delimiters between classnames

If you'd like to have extra delimieters between the rendered classnames for clarity, you can use a

class_delimiter
setting:
- set_bemto_settings({ class_delimiter: '|' })

+b.foo.bar_baz

Would be rendered as

Note that there would be always added spaces around the given delimiter, so you don't need to include them in the setting's value.

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 Pug 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

Foo

Github

Here I am

Ah, I'm not a link

Github

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.

To be continued!

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


Copyright (c) 2012 Roman Komarov [email protected]

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

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