You might not need a CSS preprocessor

📹 Video: https://www.youtube.com/watch?v=o2an6ON6i3g
🔥 Live slides + Demos: https://blog.hospodarets.com/you-might-not-need-a-css-preprocessor

Presented at Topconf Tallinn 2016.

Having native CSS variables, which work in all modern browsers, also mixins and nesting, we can consider switching from preprocessors to native CSS and look for a path to migration.

In the presentation, there is a description of the modern abilities of CSS, which specs are in progress, demos how this already works in browsers and how to use polyfills to make these CSS goodness work everywhere.

You will know:
1) That mostly everything you need in preprocessors currently is available in pure CSS
2) How to make it work cross-browser
3) The real examples of already migrated sites

Transcript

1. You might not need a
   CSS preprocessor
   DevDay 2016
   Serg Hospodarets
   @malyw
   

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3. No CSS
   

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4. 1996 year - CSS invented
   

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5. Content and presentation are separated
   .page-header {
   /* shorthand */
   border-bottom: 1px solid #eee;
   }
   p {
   font-family: Arial; /* font */
   font-size: 14px; /* font */
   color: #333; /* color */
   margin: 10px 0; /* layout */
   }
   .btn-outline {
   color: #563d7c; /* color */
   border-color: #563d7c; /* color */
   }
   

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6. CSS problems
   Absence of variables
   Absence of mixins
   Modules
   Nested rules are not
   supported
   Code duplication as result
   

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7. Preprocessors time
   

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8. Solved by
   preprocessors
   

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9. Sass:
   Variables and Operators (+, -, *, /, %)
   $font-size: 10px;
   $font-family: Helvetica, sans-serif;
   body {
   font: $font-size $font-family;
   }
   .mark{
   font-size: 1.5 * $font-size;
   }
   

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10. Mixins
    @mixin clearfix {
    &:after {
    display: block;
    content: '';
    clear: both;
    }
    }
    .sidebar{
    @include clearfix;
    }
    .main{
    @include clearfix;
    }
    .sidebar:after {
    display: block;
    content: '';
    clear: both;
    }
    .main:after {
    display: block;
    content: '';
    clear: both;
    }
    

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11. Nesting
    HTML SCSS
    
    
    
    link
    
    
    
    dropdown link
    
    
    
    
    // menu
    .nav {
    > li {
    > a:hover {
    background-color: red;
    }
    // submenu
    > ul {
    background-color: #fff;
    > li > a:hover {
    background-color: black;
    }
    }
    }
    }
    

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12. Modules
    

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13. What we use today
    

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14. Preprocessors
    problems
    

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15. Additional setup is needed to make a compiler work
    Any change require recompilation
    Compilation takes time ⏰
    

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16. Each has own syntax!
    // Sass
    $color: #f00;
    $images: "../img";
    @mixin clearfix {
    &:after {
    content: " ";
    display: block;
    clear: both;
    }
    }
    body {
    color: $color;
    background: url("#{img}/1.png");
    @include clearfix;
    }
    // Less
    @color: #f00;
    @images: "../img";
    .clearfix() {
    &:after {
    content: " ";
    display: block;
    clear: both;
    }
    }
    body {
    color: @color;
    background: url("@{img}/1.png");
    .clearfix;
    }
    

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17. Source maps are required
    Debug might be hard (or buggy)
    

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18. We want
    Variables
    Mixins
    Nesting
    Modules
    Selector helpers, color functions
    We don't want
    Additional setup
    Compilation
    Not standardized syntax
    Hard debug
    

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19. Does CSS have all this
    today?
    Let's take a look
    

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20. What we want?
    Variables
    

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21. First CSS variable currentColor
    :root { color: red; }
    i {border: 1px solid currentColor;}
    :root { color: red; }
    i {border: 1px solid red;}
    Other "variables": em, rem
    html { font-size: 1em; }
    h1 { font-size: 2.074em; }
    @media (min-width: 1400px) {
    html { font-size: 1.25em; }
    }
    html { font-size: 16px; }
    h1 { font-size: 33px; }
    @media (min-width: 1400px) {
    html { font-size: 20px; }
    h1 { font-size: 41px; }
    }
    

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22. (a.k.a. CSS variables)
    CSS custom properties
    

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23. View Slide

24. Good news!
    

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25. Syntax
    /* declaration */
    --VAR_NAME: ;
    /* usage */
    var(--VAR_NAME)
    /* root element selector (global scope), e.g. */
    :root {
    /* CSS variables declarations */
    --main-color: #ff00ff;
    --main-bg: rgb(200, 255, 255);
    }
    body {
    /* use the variable */
    color: var(--main-color);
    }
    Didn't expect the "--"? There was .
    a reason
    

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26. Variable examples
    :root{
    --main-color: #4d4e53;
    --main-bg: rgb(255, 255, 255);
    --logo-border-color: rebeccapurple;
    --header-height: 68px;
    --content-padding: 10px 20px;
    --base-line-height: 1.428571429;
    --transition-duration: .35s;
    --external-link: "external link";
    --margin-top: calc(2vh + 20px);
    }
    And even..
    :root{
    --foo: if(x > 5) this.width = 10;
    }
    

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27. Variable Defaults
    If the variable has already been assigned to
    - it won’t be re-assigned
    p {
    --p-margin: 5px;
    margin: var(--p-margin, 0 0 10px); /* 5px */
    }
    If it doesn’t have a value yet
    - it will be given one.
    p {
    margin: var(--p-margin, 0 0 10px);/* 0 0 10px */
    }
    

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28. Reassign vars from others
    .block {
    --block-text: 'This is my block';
    --block-highlight-text: var(--block-text)' with highlight';
    }
    .block__highlight:before {
    content: var(--block-highlight-text);
    /*This is my block with highlight*/
    }
    

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29. Reset/inherit values
    As for any other CSS property, you can apply "initial" and
    "inherit" values
    .with-reset {
    --bgcolor: initial;/* RESETS THE VALUE for the scope */
    --color: green;/* CHANGES THE VALUE */
    --border: inherit;/* INHERITS THE VALUE for the scope */
    }
    

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30. Usage example: emulating non existing CSS rule
    

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31. Scopes
    
    My block is
    awesome
    
    Follow usual CSS cascade rules:
    :root{
    --global-var: 1em;
    /* --global-var is available globally */
    }
    .block {
    --block-var: 1.5em;
    /* --global-var and --block-var are available */
    }
    .block__highlight {
    --block-highlight-var: 2rem;
    /* --global-var , --block-var and --block-highlight-var */
    font-size: var(--block-highlight-font-size);
    }
    

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32. CSS / preprocessors scopes are different
    /* SCSS: scope depends on
    the selectors structure
    in the code */
    $font-size: 20px;
    .block{
    $font-size: 42px;
    }
    .block__highlight{
    font-size: $font-size;
    }
    /* CSS: scope depends
    on the selectors structure
    in the DOM */
    :root{
    --font-size: 20px;
    }
    .block{
    --font-size: 42px;
    }
    .block__highlight{
    font-size: var(--font-size);
    }
    

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33. Scope examples
    /* Global scope (usually

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34. Variables are alive
    

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35. Operators and calculations
    :root {
    --block-font-size: 1rem;
    }
    .block__highlight {
    /* DOESN'T WORK */
    font-size: var(--block-font-size)*1.5;
    }
    CSS calc( ) to the rescue (for values)!
    :root {
    --block-font-size: 1rem;
    }
    .block__highlight {
    /* WORKS */
    font-size: calc(var(--block-font-size)*1.5);
    }
    

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36. Generate colors from CSS custom properties
    

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37. CSS to JS: without
    To pass variables from CSS to JS we used to use
    to write JSON in CSS
    workarounds or hacks
    .breakpoints-data {
    font-family: '{"phone":"480px","tablet":"800px"}';
    }
    

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38. CSS to JS: with
    .breakpoints-data {
    --phone: 480px;
    --tablet: 800px;
    }
    JS
    const breakpointsData = document.querySelector('.breakpoints-data');
    // GET
    const phone = getComputedStyle(breakpointsData)
    .getPropertyValue('--phone');
    // SET
    breakpointsData.style
    .setProperty('--phone', 'custom');
    

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40. Check if supported
    CSS
    @supports ( (--a: 0)) {
    /* supported */
    }
    @supports ( not (--a: 0)) {
    /* not supported */
    }
    JS
    const isSupported = window.CSS && window.CSS.supports &&
    window.CSS.supports('--a', 0);
    /* e.g. load a CSS file generated by a preprocessor */
    if(!isSupported){
    removeCss('css-custom-properties.css')
    loadCss('without-css-custom-properties.css');
    }
    

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41. Why else CSS Custom Props are
    better?
    

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42. Color schema switcher based on CSS custom property
    values
    Cannot be done by a preprocessor without generating additional code
    

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43. What do we want?
    Mixins
    

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44. (a.k.a. CSS mixins)
    CSS Custom Sets of Properties and
    @apply rule
    

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45. Custom Property:
    :root{
    /* --property: value; */
    --VAR: ;
    }
    Custom properties can hold more than just values- they can
    also be used to hold sets of declarations:
    :root{
    /*
    --property: {
    property1: value1;
    property...: value...;
    }
    */
    --MIXIN: {
    /* style declaration 1 */
    /* style declaration ... */
    };
    }
    

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46. Syntax
    :root {
    --pink-schema: {
    color: #6A8759;
    background-color: #F64778;
    }
    }
    body{
    @apply --pink-schema;
    }
    @apply rule takes these sets of declarations and inlines
    them in another style rule
    

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47. Reasons to use
    Put reusable bunches of styles into separate entities
    Avoid code duplication
    Apply changes in a central place
    Behavior
    Everything form CSS variables (scopes, usage from JS etc.) is
    applicable for Custom Sets of Properties
    

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48. Examples
    :root {
    --clearfix: {
    display: table;
    clear: both;
    content: '';
    };
    }
    .clearfix:after{
    @apply --clearfix;
    }
    :root {
    --overflow-ellipsis: {
    overflow: hidden;
    text-overflow: ellipsis;
    white-space: nowrap;
    };
    }
    .overflow-box{
    @apply --overflow-ellipsis;
    }
    

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49. (try in Chrome Canary)
    CSS Triangle Mixin
    

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50. Problem- variables cannot be passed
    :root {
    --triangle-to-bottom-size: 50px;
    --triangle-to-bottom: {
    /* STYLES */
    border-bottom-width: var(--triangle-to-bottom-size);
    };
    }
    .triangle-to-bottom {
    --triangle-to-bottom-size: 8px;
    @apply --triangle-to-bottom;
    /* but still 50px size is applied for border-bottom-width */
    }
    Discussion to change this behavior is in progress
    

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51. Mixins for CSS vendor prefixes?
    Every time you need clip-path:
    Lea Verou's idea:
    * {/* has zero specificity */
    /* prevents the property inheritance from outer scopes */
    --clip-path: initial;
    -webkit-clip-path: var(--clip-path);
    clip-path: var(--clip-path);
    }
    header {/* any selector like this overrides the "*" */
    /* assign the prop value for the scope */
    --clip-path: polygon(0% 0%, 100% 0%, 100% 100%%, 0% 100%);
    }
    

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52. What we need?
    Nesting
    

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53. What we want to avoid?
    CSS code duplication in selectors
    Bad readability of the code
    table.colortable td {
    text-align:center;
    }
    table.colortable td.upper {
    text-transform:uppercase;
    }
    table.colortable td:first-child,
    table.colortable td:first-child+td {
    border:1px solid #000;
    }
    

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54. Tab Atkins' CSS Nesting spec
    proposal
    Syntax is close to preprocessors
    /* Dropdown menu on hover */
    ul {
    /* direct nesting (& MUST be the first part of selector)*/
    & > li {
    color: #000;
    & > ul { display: none; }
    &:hover {
    color: #f00;
    & > ul { display: block; }
    }
    }
    }
    

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55. The Nesting At-Rule: '@nest' for complex cases
    @nest < selector (MUST CONTAIN a nesting selector '&') >
    .foo {
    color: black;
    @nest body.loading & {
    opacity: 0.5;
    }
    @nest :not(&) {
    color: white;
    }
    }
    .foo {
    color: black;
    }
    body.loading .foo {
    opacity: 0.5;
    }
    :not(.foo) {
    color: white;
    }
    

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56. Migration is easy
    Nesting selector syntax is very close to Sass
    Complex nesting can be done using @nest at-rule
    media expression etc. are nested:
    a {
    @media (min-width: 30em) {
    color: yellow;
    }
    }
    @media (min-width: 30em) {
    a {
    color: yellow
    }
    }
    

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57. What we wish?
    Modules
    

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58. The @import CSS at-rule is used to import style rules from
    other style sheets.
    It is available in all browsers since IE 5.5!
    

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60. Why we didn't use this before?
    Bugs in old browsers with the order of inclusion
    Before requests didn't go in parallel
    For HTTP1x good practice is file concatenation.
    With coming of HTTP2 rules will be cnanged.
    

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61. You can easily apply media queries for different stylesheets.
    Advantages for free:
    Conditional loading
    /* Formal syntax */
    @import [ | ] []?;
    @import url("print.css") print;
    @import "mobile.css" (max-width: 728px);
    The linked resources are loaded only when condition is met.
    

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62. We have
    Variables, Mixins
    Nesting and Modules
    What else we want?
    Selector helpers for complex cases
    Color functions
    

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63. pseudo-class
    :matches
    /* SYNTAX */
    :matches( selector[, selector]* )
    A functional pseudo-class taking a selector list as its
    argument.
    .nav:matches(.side,.top) .links:matches(:hover, :focus) {
    color: #BADA55;
    }
    /* Same thing as this... */
    .nav.side .links:hover,
    .nav.top .links:hover,
    .nav.side .links:focus,
    .nav.top .links:focus {
    color: #BADA55;
    }
    

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64. @custom-selector
    /* SYNTAX */
    @custom-selector: ;
    Example:
    @custom-selector :--text-inputs input[type="text"],
    input[type="password"];
    :--text-inputs.disabled,
    :--text-inputs[disabled] {
    opacity: 0.5
    }
    Same as:
    input[type="text"].disabled,
    input[type="password"].disabled,
    input[type="text"][disabled],
    input[type="password"][disabled] {
    opacity: 0.5
    }
    

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65. Color functions
    /* SYNTAX */
    color( * )
    some adjusters have shortcuts
    adjusters can be pipped
    color(
    red /* from red */
    blackness(+25%) /* to 25% more black than red */
    blackness(+25%) /* to 50% more black than red */
    blackness(-50%) /* to red again */
    hue(+ 30deg) /* to orange */
    hue(- 30deg) /* to red again */
    );
    

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67. Better media queries!
    Problem
    The syntax is too long and they cannot be reused easily
    Need
    A simple way to set breakpoints and reuse them
    

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68. Media Queries Level 4:
    Custom media queries
    /* SYNTAX */
    @custom-media --NAME ;
    How to use:
    @custom-media --tablet (min-width: 800px) and (max-width: 1024px);
    @media (--tablet){
    .custom-media-queries{
    background-color: red;
    }
    }
    

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69. Instead of:
    Use:
    Media queries ranges
    @media (min-width: 800px) and (max-width: 1024px) {
    .media-queries-range{
    background-color: red;
    }
    }
    @media (width >= 800px) and (width <= 1024px) {
    .media-queries-range{ background-color: red; }
    }
    With custom media queries:
    @custom-media --tablet (width >= 800px) and (width <= 1024px);
    @media (--tablet){
    /* STYLES */
    }
    

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70. Can we Use it now?
    Current situation
    CSS variables are supported in all the modern browsers
    except EDGE
    CSS mixins work in Chrome Canary
    Some of other specs are integrated in various browsers,
    sometimes it's in beta/dev versions
    Should we wait for another couple years?
    

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72. PostCSS based
    Includes other PostCSS plugins (vars, mixins etc.)
    If you already use Autoprefixer- change is straign forward
    Build setup:
    //...
    postcss: {
    options: {
    processors: [
    require('autoprefixer')({
    browsers: ['last 2 versions']
    })
    ]
    },
    //...
    //...
    postcss: {
    options: {
    processors: [
    require('postcss-cssnext')({
    browsers: ['last 2 versions']
    })
    ]
    },
    //...
    

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73. How to migrate
    1) Preprocessor
    Add PostCSS and cssnext
    2) Preprocessor+PostCSS+ability to use new CSS features
    Change vars, mixins, media queries, colors and selectors to the CSS ones
    Disable a preprocessor
    3) PostCSS + all the CSS additions power
    Disable cssnext and PostCss when the browsers support everything
    4) You have pure CSS with everything
    

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74. You still can combine preprocessor and all the mentioned
    CSS additions (or process them via PostCSS) to use the
    strongest parts of the both.
    

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75. Any live sites which use all these
    new CSS features?
    blog.hospodarets.com
    

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76. View Slide

77. Conclusions
    Today we have mostly everything we need from
    preprocessors in pure CSS
    variables, mixins
    modules, nesting
    complex selectors and color functions
    We have polyfills to make it work until it's supported in all
    browsers
    We have the real examples of migrated applications
    

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78. How can I help / stay tuned?
    Spec, dra s, proposals
    CSS Working Group (WG) Editor Dra s
    Tab Atkins spec proposals
    Other
    Subscribe to CSS Working Group mailing list / RSS etc.
    cssnext issues
    

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79. Thank you!
    @malyw
    

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