BEM it!

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BEM Methodology for small companies with high expectations

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BEM it!

  1. 1. by Max Shirshin Frontend Team Lead, Deltamethod Consultant, Yandex BEM it! BEM Methodology for small companies with high expectations
  2. 2. Why bother?
  3. 3. Web development needs: ● Methodologies, not frameworks ● Same entities across different technologies ● Scalability
  4. 4. BEM to the rescue
  5. 5. What is BEM? “BEM claims that three basic entities (Blocks, Elements, and Modifiers) are enough to define the way you author HTML / CSS / JavaScript, structure code and components, set up interaction and scale your project to build an industry-leading service.”
  6. 6. What is BEM? ● A methodology “Theoretical underpinning” for methods and best practices
  7. 7. What is BEM? ● A methodology “Theoretical underpinning” for methods and best practices ● Originally introduced by Yandex — www.yandex.ru (English: www.yandex.com) — 200+ Yandex services using full BEM stack (methodology + tools) — 19 million users daily audience
  8. 8. What is BEM? ● A methodology “Theoretical underpinning” for methods and best practices ● Originally introduced by Yandex — www.yandex.ru (English: www.yandex.com) — 200+ Yandex services using full BEM stack (methodology + tools) — 19 million users daily audience ● Used by external projects — other services — tools / libraries
  9. 9. Some theory :-)
  10. 10. What is BEM? BLOCK – Standalone part of an interface: ● button ● text field ● flyout ● heading ● menu
  11. 11. What is BEM? BLOCK – Standalone part of an interface: ● button ● text field ● flyout ● heading ● menu – Re-usable in different contexts – Self-sufficient
  12. 12. What is BEM? ELEMENT – An integral part of a block: ● button ● text field ● flyout ● heading ● menu
  13. 13. What is BEM? ELEMENT – An integral part of a block: ● button icon ● text field label ● flyout title ● heading logo ● menu item
  14. 14. What is BEM? ELEMENT – An integral part of a block: ● button icon ● text field label ● flyout title ● heading logo ● menu item – No standalone meaning outside of a block – Some blocks have no elements
  15. 15. What is BEM? MODIFIER – Defines property or state on a block or element: ● button ● text field ● flyout ● heading ● menu item
  16. 16. What is BEM? MODIFIER – Defines property or state on a block or element: ● button color ● text field disabled state ● flyout alignment ● heading level ● menu item bullet type
  17. 17. What is BEM? MODIFIER – Defines property or state on a block or element: ● button color ● text field disabled state ● flyout alignment ● heading level ● menu item bullet type – Multiple modifiers may co-exist on a single block/element
  18. 18. BEM + DOM ● Blocks are mapped to DOM
  19. 19. BEM + DOM ● Blocks are mapped to DOM ● Blocks/elems/mods are denoted with CSS classes
  20. 20. BEM + DOM ● Blocks are mapped to DOM ● Blocks/elems/mods are denoted with CSS classes ● DOM nodes can be “shared”: you can mix (block1 + block2) or (element1 + block2) on a same node
  21. 21. BEM markup forms a semantic overlay over the existing DOM structure. This overlay is called a BEM tree.
  22. 22. BEM HOWTO for your beloved project with benefits explained
  23. 23. HOWTO: HTML / CSS
  24. 24. CSS naming conventions “BEM uses CSS class names to denote blocks, elements and modifiers.”
  25. 25. CSS naming conventions BLOCK .b-button .b-text-field .b-flyout .b-heading .b-menu
  26. 26. CSS naming conventions <ul class=”b-menu”> <li> <a href=”/more”>Read More</a> </li> <li> <a href=”/buy”>Buy Online</a> </li> <li> <a href=”/buy”>Contact</a> </li> </ul>
  27. 27. CSS naming conventions ELEMENT .b-button__icon .b-text-field__label .b-flyout__title .b-heading__logo .b-menu__item
  28. 28. CSS naming conventions <ul class=”b-menu”> <li class=”b-menu__item”> <a href=”/more”>Read More</a> </li> <li class=”b-menu__item”> <a href=”/buy”>Buy Online</a> </li> <li class=”b-menu__item”> <a href=”/buy”>Contact</a> </li> </ul>
  29. 29. CSS naming conventions MODIFIER .b-button_color_blue .b-text-field_disabled .b-flyout_align_top .b-heading_level_alpha .b-menu__item_pos_first
  30. 30. CSS naming conventions <ul class=”b-menu b-menu_horizontal”> <li class=”b-menu__item”> <a href=”/more”>Read More</a> </li> <li class=”b-menu__item”> <a href=”/buy”>Buy Online</a> </li> <li class=”b-menu__item”> <a href=”/buy”>Contact</a> </li> </ul>
  31. 31. CSS naming conventions <ul class=”b-menu b-menu_horizontal”> <li class=”b-menu__item b-menu__item_pos_first”> <a href=”/more”>Read More</a> </li> <li class=”b-menu__item”> <a href=”/buy”>Buy Online</a> </li> <li class=”b-menu__item”> <a href=”/buy”>Contact</a> </li> </ul>
  32. 32. Additional notes on CSS ● Page (Document) is also a block
  33. 33. Additional notes on CSS ● Page (Document) is also a block ● Layouts are blocks (same rules apply)
  34. 34. Additional notes on CSS ● Page (Document) is also a block ● Layouts are blocks (same rules apply) ● No CSS outside of blocks
  35. 35. Additional notes on CSS ● Page (Document) is also a block ● Layouts are blocks (same rules apply) ● No CSS outside of blocks ● No common CSS resets (block independency!)
  36. 36. Additional notes on CSS ● Page (Document) is also a block ● Layouts are blocks (same rules apply) ● No CSS outside of blocks ● No common CSS resets (block independency!) ● No “shared” styles (no need)
  37. 37. Additional notes on CSS ● Page (Document) is also a block ● Layouts are blocks (same rules apply) ● No CSS outside of blocks ● No common CSS resets (block independency!) ● No “shared” styles (no need) ● DOM tree → BEM tree
  38. 38. Benefits! Drop tag names and IDs
  39. 39. Benefits! Drop tag names and IDs ● Faster selectors ● Re-use same semantic block on: — <DIV class=”b-block”> — <SPAN class=”b-block”> — <TABLE class=”b-block”>
  40. 40. Benefits! CSS specificity magic solved
  41. 41. Benefits! CSS specificity magic solved Priority of CSS rules: by specificity first, then by rule order
  42. 42. Benefits! CSS specificity magic solved Priority of CSS rules: by specificity first, then by rule order td.odd { background-color: gray } td.even { background-color: white } .highlighted { background-color: yellow } <TD class="odd highlighted"> <!-- Still gray, baby :-( --> </TD>
  43. 43. Benefits! CSS specificity magic solved Priority of CSS rules: by specificity first, then by rule order td.odd { background-color: gray } td.even { background-color: white } td.highlighted { background-color: yellow } <TD class="odd highlighted"> <!-- This works, I'm yellow now --> </TD>
  44. 44. Benefits! Bye-bye CSS cascade?!
  45. 45. Benefits! Bye-bye CSS cascade?! Only one CSS class needed to: ● style a block container ● style any element within a block ● add extras/overrides with a modifier Doesn't it cover 90% of your styling needs?
  46. 46. Benefits! Bye-bye CSS cascade?! ...well, not exactly. Example of an element affected by a block modifier: /* hide labels for disabled text fields */ .b-text-input_disabled .b-text-input__label { display: none; }
  47. 47. HOWTO: JavaScript
  48. 48. JavaScript Components → Blocks Work with BEM tree, not DOM tree
  49. 49. JavaScript jQuery BEM plugin http://xslc.org/jquery-bem/ ● Extends jQuery Sizzle with selectors for BEM entities (mix them with “normal” selectors) ● Add callbacks on modifiers set/change ● Supports methods tied to blocks/elements
  50. 50. JavaScript i-bem.js framework by Yandex + tutorial https://github.com/toivonen/bem-js-tutorial ● First English draft docs (expect more!) ● 100% BEM-based declarative API ● Part of a larger bem-core library
  51. 51. JavaScript Twitter Flight (used by Deltamethod) http://flightjs.github.io ● Self-contained components, 100% event-driven ● Based on jQuery; AMD-friendly; BEM-friendly ● Built-in syntax sugar for predefined selectors (good for BEM tree) ● [Shameless self-promo] Try Flight with Reggirt: http://github.com/ingdir/reggirt jQuery plugin that emulates event capturing (opposite of event bubbling)
  52. 52. JavaScript Twitter Flight (used by Deltamethod) http://flightjs.github.io ● Self-contained components, 100% event-driven ● Based on jQuery; AMD-friendly; BEM-friendly ● Built-in syntax sugar for predefined selectors (good for BEM tree) ● [Shameless self-promo] Try Flight with Reggirt: http://github.com/ingdir/reggirt jQuery plugin that emulates event capturing (opposite of event bubbling)
  53. 53. Benefits! HTML is no longer semantic. JavaScript is.
  54. 54. HOWTO: Design / UX
  55. 55. BEM is the universal language for developers and designers, the bridge across technology gaps.
  56. 56. UX + Frontend ● Design a style guide
  57. 57. UX + Frontend ● Design a style guide ● Keep it up-to-date
  58. 58. UX + Frontend ● Design a style guide ● Keep it up-to-date, always!
  59. 59. UX + Frontend ● Design a style guide ● Keep it up-to-date, always! ● Build new screens quickly
  60. 60. UX + Frontend Build your block library. The code itself is the styleguide.
  61. 61. Benefits! ● Prototyping mapped to code from day 1
  62. 62. Benefits! ● Prototyping mapped to code from day 1 ● Code mapped to prototypes from day 1
  63. 63. HOWTO: File structure
  64. 64. File and folder structure Flat block structure with a folder for each block. Simple structure for BEM beginners: /b-block block.css block.js block.tpl ...whatever you need
  65. 65. File and folder structure Advanced structure to expose semantics /block /css block.css block__elem1.css block__elem2.css block_mod.css /js block.js /template block.tpl block__elem1.tpl block__elem2.tpl
  66. 66. File and folder structure Advanced structure to expose semantics /block /css block.css block__elem1.css block__elem2.css block_mod.css /js block.js /template block.tpl block__elem1.tpl block__elem2.tpl
  67. 67. Benefits! ● Unified structure for automation ● Redefinition levels: different libraries, same structure /common /b-block /css block.css /template block.tpl /app1 /b-block /css block__elem1.css /js block.js /template block__elem1.tpl +
  68. 68. Build process and deployment Use a build tool! Borschik: an open-source build tool by Yandex Code: https://github.com/bem/borschik English docs: http://bem.info/articles/borschik
  69. 69. max.shirshin@gmail.com http://gplus.to/ingdir @ingdir maxshirshin Thank you!
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