BEM Methodology Jacek Spławski

Poznań, January 2016

We are not designing pages, we are designing systems of components.

— Stephen Hay

Modularity is requirement of maintainable systems.

— Ben Callahan

OOCSS / SMACSS / BEM / Atomic / SUITCSS

BEM is a naming convention for classes in HTML and CSS.

Created by Yandex — one of the leading internet companies in Russia.

Block Element Modifier

Block is standalone entity that is meaningful on its own.

Blocks can be nested and interact with each other, semantically they remain equal; there is no precedence or hierarchy.

Block names may consist of lowercase Latin letters, digits, and dashes. Individual

words within names are separated by a dash.

.block

Block name should identify block and say what it is responsible for. The block name

replaces IDs.

Element is parts of a block and have no standalone meaning. They are semantically tied to its block.

Element names may consist of Latin letters, digits, dashes and underscores. CSS class is formed as block name plus

two underscores plus element name.

.block__element

Modifier are flags on blocks or elements. Use them to change appearance or

behavior.

Modifier names may consist of Latin letters, digits, dashes and underscores.

CSS class is formed as block’s or element’s name plus two dashes.

.block__element——modifier

DOM Tree → BEM Tree

Sass ♥ BEM

.block { &——modifier {} &__element {} }

=

.block {}

.block——modifier {}

.block__element {}

BEM ? JS

jQuery BEM Helpers jQuery BEM Plugin i-BEM framework by Yandex

no dependencies on other elements reduce cascading problems reduce amount of CSS code create ready blocks library simple and understandable structure in CSS and HTML code Sass loves BEM drop tag names and IDs

long class names which could look’s weird develop the habit to properly name class modular thinking

https://css-tricks.com/bem-101/ http://getbem.com/ https://en.bem.info/https://www.smashingmagazine.com/2012/04/a-new-front-end-methodology-bem/