maintainable frontend development with bem
Post on 22-Jun-2015
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UI Framework Team Lead
Maintainable Frontend Development with BEM
Varvara Stepanova
#b_
It's me
3
4
Search
Images Video Realty Social
Blogs Apps Jobs
Maps Mail Marketplace etc.
Next 30 minutes
• Usual development cycle• Main problems it brings• BEM solutions to the problems• New development workflow• Recently happened in BEM world
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Usually
Usual development cycle and problems
7
Usual development cycle and problems
• decomposition – every time• every change starts from zero• cannot reuse your own work
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BEM is a world on its own
• methodology of modularity• file structure recommendations• reusable libraries• helpful tools & optimizers• template engine
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Block • Element • Modifier
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Block is an independent component
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Page of blocks
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page.html
<body class="page">
<div class="header"> <img class="logo" ... /> <div class="search">...</div> <div class="menu">...</div> </div>
<div class="layout"> <div class="sidebar">...</div> <div class="menu">...</div> </div>
</body>
Some blocks have elements
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Block with elements
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page.html
<div class="tabbed-pane"> <ul> <li class="tabbed-pane__tab">Tab1</li> <li class="tabbed-pane__tab">Tab2</li> </ul> <div class="tabbed-pane__panel"> ... </div></div>
Elements
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Block of elements
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Modifiers change blocks and elements
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<div class=" tabbed-pane tabbed-pane_theme_blue"> <!-- // --></div>
<div class=" tabbed-pane tabbed-pane_to_bottom"> <!-- // --></div>
Block • Element • Modifier
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1. Ever-changing layout
2. No copy-paste
3. Unified semantic
What do we want?
1. Ever-changing layout
Independent CSS blocks
• are not affected by parents• do not affect children
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Independent CSS blocks
• a block has its nameNot id but classname selectors
• no tag selectors• avoid cascade
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Cascade: a way to express dependency
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CSS
.header a { text-decoration: none;}.main .photo { width: 150px; height: 150px;}.sidebar li { list-style: none; display: inline-block; padding: 0 0.5em;}
div.big_form .photo { width: 250px; height: 250px;}
.big_form .photo { width: 500px !important;}
«
Improving rendering performance
The style system matches rules by starting with the key selector, then moving to the left (looking for any ancestors in the rule’s selector).
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David Hyatt, MDN
mzl.la/UuwZql
Who uses the method
• Yandexbit.ly/bem-riga-2012
• GitHubbit.ly/github-css
• Harry Robertsinuitcss.com
• OOCSS, SMACSS, etc.
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2. No copy-paste
Each block is a separate CSS file
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blocks/
search.css search__checkbox.css search__autocomplete.css
tabbed-pane.css tabbed-pane__tab.css tabbed-pane__panel.css
menu.css menu__item.css menu_size_big.css
book.css book__title.css
...taken when you need it!
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CSS
@import url(blocks/header.css);@import url(blocks/search.css);@import url(blocks/tabbed-pane.css);@import url(blocks/tabbed-pane__tab.css);@import url(blocks/tabbed-pane__panel.css);@import url(blocks/book.css);@import url(blocks/book__image.css);@import url(blocks/menu.css);@import url(blocks/menu_size_big.css);@import url(blocks/menu__item.css);@import url(blocks/footer.css);
Easy to share
• email to a friend• version control systems
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Linking library to projects
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search maps market
Services are using two block levels
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search marketmaps
Project file structure with a library linked
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library/ # by linking a remote repo header.css footer.css menu.css ...
blocks/ header.css books.css vote.css
library/header.css
Redefining in CSS
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.header {
color: red;
}
blocks/header.css
.header {
color: green;
}
Pick up from two levels
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CSS
@import url(library/blocks/header.css);
@import url(library/blocks/search.css);@import url(blocks/search.css);
@import url(library/blocks/tabbed-pane.css);@import url(library/blocks/tabbed-pane__tab.css);@import url(library/blocks/tabbed-pane__panel.css);@import url(blocks/book.css);@import url(blocks/book__image.css);@import url(library/blocks/menu.css);
Automation
• Make• Rake• Grunt
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3. Unified semantic
Unified semantic
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Different implementations
Block: CSS + JavaScript
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blocks/
book/ book.css menu/ menu.css menu.js menu__item.css
search/ search.css
tabbed-pane/ tabbed-pane.css tabbed-pane.js
Block: many technologies
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tabbed-pane/ tabbed-pane.css tabbed-pane.js tabbed-pane.xsl
logo/ logo.png logo.css logo.xsl
search/ search__autocomplete.css search__autocomplete.js search.css search.js search.xsl
Block: several templating solutions
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tabbed-pane/ tabbed-pane.css tabbed-pane.js tabbed-pane.xsl tabbed-pane.bemhtml
logo/ logo.png logo.css logo.xsl logo.bemhtml
search/ search__autocomplete.css search__autocomplete.js search.css search.js search.xsl search.bemhtml
Block: documentation
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tabbed-pane/ tabbed-pane.css tabbed-pane.js tabbed-pane.bemhtml tabbed-pane.md
logo/ logo.png logo.css logo.bemhtml logo.md
search/ search__autocomplete.css search__autocomplete.js search__autocomplete.md search.css search.js search.bemhtml search.md
Services are using two block levels
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search marketmaps
New dev workflow
Breaking an interface into blocks
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Fix. Grow. Improve.
• single language• blocks are easy to add/move/remove• maintainability• non-stop refactoring ;-)
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Do we like what robots like?
Nice development tools
• BEM tools to build pages• Borschik to flatten the CSS and JS files• CSSO to optimize
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index.css
@import url(blocks/header/header.css);@import url(blocks/menu/menu.css);...
CSS flattening with Borschik
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_index.css
.header { ...}.menu { ...}
index.js
/*borschik:include:blocks/menu/menu.js*//*borschik:include:blocks/tabbed-pane/tabbed-pane.js*/...
JavaScript flattening with Borschik
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_index.js
/* Menu block begins */(function($) { $('.menu__item').on('click', function(e) { $(this).toggleClass('menu__item_state_current'); });})(jQuery);
Nice development tools
• BEM tools to build pages• Borschik to flatten the CSS and JS files• CSSO to optimize
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Optimizing with CSSO
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DEVELOPMENT
.header { color: red;}
.header { color: green;}
PRODUCTION
.header { color: green;}
bem.info/tools
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Recently in BEM world
bit.ly/bem-history
The evolution of BEM
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by Max Shirshin and Vitaly Harisov
Several block libraries
• common library of 100+ blocks• distinct libraries
– search services– map services– image services
...
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Linking several libraries to a project
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common-lib/ header/ footer/ layout/ ...
search-lib/ header/ search-form/ ...
maps-lib/ map/ map-point/ ...
blocks/ books/ header/ map-point/ ...
Any library needs...
• web site– documentation– block examples
• release workflow– changelogs– unit tests
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What to do with BEM?
• follow recommendations– modular everything (CSS, JS, etc.)– file structure– building projects
• participate• write your own libraries
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http://bem.info
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toivonen@yandex-team.ru
Varvara StepanovaUI Framework Team Lead
@toivonens@bem_tw
Thank you
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