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Dirty Tricks From Dark
Corners Of Front-End
Vitaly Friedman
August 25th, 2016 • Reykjavik, Iceland
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Vitaly Friedman, editor-in-chief
and co-founder of SmashingMag
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Front-End Challenges
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“What if you want to nest one link
inside another? E.g. in sidenotes,
footnotes or articles, when you
want the entire excerpt to be linked,
but the excerpt could potentially
also contain links which you can’t
strip out from the markup?
— Roman Komarov
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• HTML:
When the crisis was over,
Mr. Jones
left the region immediately.
• Browser parser reads it as:
When the crisis was over,
Mr. Jones
left the region immediately.
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• Browser parser reads it as:
When the crisis was over,
Mr. Jones
left the region immediately.
• HTML:
When the crisis was over,
Mr. Jones
left the region immediately.
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• Browser parser reads it as:
When the crisis was over,
Mr. Jones
left the region immediately.
• HTML:
When the crisis was over,
Mr. Jones
left the region immediately.
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• Browser parser reads it as:
When the crisis was over,
Mr. Jones
left the region immediately.
• HTML:
When the crisis was over,
Mr. Jones
left the region immediately.
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• Browser parser reads it as:
When the crisis was over,
Mr. Jones
left the region immediately.
• HTML:
When the crisis was over,
Mr. Jones
left the region immediately.
• Works well in modern browsers:
IE 9+, Firefox 4+, Opera 9+, Safari 5.1+, Chrome 14+.
For old IE, we can use Cond. comments inside .
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SVG Embedding
• 
, background: url(image.svg);
block access to SVG paths via CSS.
• With “inline” SVG or Data URI encoding we can
style SVG via CSS and avoid one HTTP-request.
, background: url(image.svg);
block access to SVG paths via CSS.
• With “inline” SVG or Data URI encoding we can
style SVG via CSS and avoid one HTTP-request.
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SVG Embedding
• With “inline” SVG or Data URI encoding we can
style SVG via CSS and avoid one HTTP-request.
• Alternative: using SVG as an avoids
caching issues with CSS styling within SVG.
…
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“By default, broken images look
pretty unspectacular. Is there any
way to improve the experience by
changing the styling if images are
actually broken?
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The ![]()
element is a replaced
element. This is an element “whose
appearance and dimensions are
defined by an external resource.
Pseudo-elements typically
shouldn’t work with it.
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“To achieve fluid typography, we can
combine the calc( ) function in CSS
with viewport units (vw/vh/vmin/
vmax). But what if you want to
apply a modular scale to font sizes?
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We can get perfectly fluid type with
html { font-size: calc(1em + 1vw); }
but it gives us little control over the
rate at which viewport units change.
Media queries? Well, with them
usually there is an annoying “visual”
jump between fixed and fluid values.
— Mike Riethmuller
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…E.g. if we wanted to choose a font-
size of 16px at a screen resolution of
400px and then transition to 24px at
a resolution of 800px, we couldn’t
do it without a breakpoint.
— Mike Riethmuller
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You choose the min and max font-
size and the screen sizes, over which
the font should scale and plug them
into the equation. You can use any
unit type including ems, rems or px.
— Mike Riethmuller
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“How do you make sure that in a
multi-column table, both a row and a
column are highlighted on hover and
on tap? Highlighting the current row
is easy, but what about the column?
— Matt Walton
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“We create tall pseudo elements on
’s with a negative top-value of
half of that value. Then we hide
these pseudo elements with oveflow:
hidden, and use negative z-index to
keep it below the content. Then we
make all cells focusable and focus
them on touchstart.
— @simurai
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• CSS:
table { overflow: hidden; }
td, th { position: relative; }
tr:hover { background-color: #ffa; }
td:hover::after { content: "";
position: absolute;
width: 100%;
height: 10000px;
left: 0;
top: -5000px;
background-color: currentColor;
z-index: -1;
}
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• CSS:
table { overflow: hidden; }
tr:hover { background-color: #ffa; }
td:hover::after,
th:hover::after { content: "";
position: absolute;
width: 100%;
height: 10000px;
left: 0;
top: -5000px;
background-color: currentColor;
z-index: -1;
}
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“Email clients, primarily Gmail,
don’t support media queries. To
build responsive email layouts, we
have to use table-layouts. But is
there a better way?
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/* “Desktop” width = 600px = 300*2 */
......
• Content Stacking
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@media only screen and (max-width: 600px) {
table, tr, td {
display: block; /* table-cell -> block */
width: 100%;
}
}
• Content Stacking
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• Column Switching
/* “Desktop” width = 600px = 300*2 */
......
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@media only screen and (max-width: 500px) {
table, tr, td {
display: block; /* table-cell -> block */
width: 100%;
}
td[class=main-col] { display: table-header-group; }
td[class=sub-col] { display: table-footer-group; }
}
• Column Switching
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/* “Desktop” width = 600px */
...
...
...
• Image Shifter
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@media only screen and (max-width: 500px) {
table, tr, td { display: block; }
td[class=image] { float: left; }
.description { clear: both; }
}
• Image Shifter
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• Order and Re-order
/* Nested tables, oh my... */
Header
Navigation
Content
Footer
/table>
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@media only screen and (max-width: 500px) {
table[class=wrapper] { display: table; }
table[class=header] { display: table-caption; }
table[class=nav] { display: block; }
table[class=content] { display: table-header-group; }
table[class=footer] { display: table-footer-group; }
}
• Order and Re-order
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HTTP/1.1 Deployment Strategy
• CSS:
.box {
width: 320px;
min-width: 480px;
max-width: 160px;
}
If the width value is greater
than the max-width value,
max-width wins.
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HTTP/1.1 Deployment Strategy
• CSS:
.box {
width: 320px;
min-width: 480px;
max-width: 160px;
}
If the min-width value is
greater than the width or
max-width values, then
min-width wins.
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HTTP/1.1 Deployment Strategy
• CSS:
.box {
display: inline-block;
min-width: 50%; // basically 2-col-desktop version
max-width: 100%; // basically 1-col-mobile version
width: calc((480px - 100%) * 480);
/* 480px = the breakpoint, 100% = width of the parent
Goal: create a value bigger than our max-width or smaller
than our min-width, so that either one of those property
is applied instead. */
}
Let’s build a 2-col-layout that
stacks and grows below 480px.
No media queries allowed.
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“You want to add a background to
inline text for headings, but the text
should be padded along both the left
and right edge of each line. The left
and right padding will only apply to
the very first and very last line.
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The box-decoration-break in CSS
specifies element’s appearance if the
box for the element is fragmented, i.e
when an inline box wraps onto
multiple lines, or when a block
spans more than one column inside
a column layout container.
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“Images make up a large portion of
bandwidth payload. Is there any
way to optimize images beyond
good ol’ image optimization? What
if a hero image has to render fast,
e.g. on landing pages?
— Tobias Baldauf
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• The original photo has 1600px width, 971 Kb.
Quality 60 brings the size down to 213 Kb.
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• Blurring unimportant parts of the photo brings
the size down to 147 Kb.
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Sequential JPEG Progressive JPEG
Images taken from http://www.pixelstech.net/article/1374757887-Use-progressive-JPEG-to-improve-user-experience 13 / 44
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Scans
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Default Scan Levels
Thanks to Frédéric Kayser for creating 'jsk': http://encode.ru/threads/1800-JSK-JPEG-Scan-Killer-progressive-JPEG-explained-in-slowmo 15 / 44
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1st Scan Layer Has Small Byte Size
Ships Fast
&
Shows Soon
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“By default, tables are quite
unpredictable and spongy, and if you
don’t know how lengthy the content
inside cells will be, some columns
can be unpredictably wide,
destroying the layout. What to do?
— Louis Lazaris
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“With table-layout: fixed; the layout
is fixed based on the first row. Set
the width of those, and the rest of
the table follows.
— Chris Coyier
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“Whenever the content is
dynamically injected into the
DOM or when “above-the-fold”
CSS is used or font changes, users
see content jumping around.
That’s particularly annoying on
small screens. Can we fix it?
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If we know the expected height of
the block, we can use min-height to
“reserve” space for it, or calculate it
with JavaScript on window early on
and write styles dynamically.
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Alternatively, we could use a
smooth transition from the initial
(fixed) height to the final (fixed)
height. Downside: transitions don’t
work on min-height.
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• CSS:
.ad-wrapper {
height: 0;
overflow: hidden;
transition: height 0.8s ease-out;
}
.ad-wrapper.loaded {
height: 400px;
}
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“What’s the deal with emoji? Can
we style them with CSS, or change
them with JavaScript? Or even
better, can they be an alternative
to SVG and icon fonts?
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Clockwise Rightwards and
Leftwards Open Circle Arrows
With Circled One Overlay
(also known as U+1F502,
🔂 or \u1f502).
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Person Raising Both Hands in
Celebration (also known as
Festivus Miracle Emoji,
U+1F64C, f64c; or \u1f64c).
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%
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Emoji are coloured glyphs added
into Unicode 6.0 in 2010. They are
depicted in the spec, but the exact
appearance isn’t defined and varies
between fonts, just like normal
typefaces display letters differently.
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Because emoji are Unicode code
points, we can create a font with the
emoji that we need in our interface
and override platform-specific
designs to avoid inconsistencies.
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Internally strings are represented
in UTF-16, so each code point can be
represented by one or more 16-bit
code units. Some emojis use only 1
code unit, others 2 and more.
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Not all emoji are created equal.
They can be modified with emoji
modifiers, so some are surrogates
which is why sometimes icons are
rendered incorrectly.
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(
)
*
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• HTML:
%
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• The browser will:
— Look up the glyph in the Sentinel font,
— If it can’t find the glyph, it will fall back to the fallback font,
— In this case, fallback is sans-serif (Helvetica/Arial),
— The fallback doesn’t have the glyph either,
— Browser will try to figure out the glyph type,
— Eventually it will look up in a locally installed Emoji font
(e.g. AppleColorEmoji),
— The browser will render the icon.
• HTML:
%
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“So you’re building a responsive
multi-lingual website that aims to
support over 30 languages. How
do you architect a system to
support this kind of complexity?
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The crucial asset of longevity is
building “neutral”, configurable
components which can be easily
extended and adjusted.
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// english.json
{
serviceName: 'english';
language: 'en';
textDirection: 'ltr';
socialMediaButtons: ['twitter', 'facebook', 'reddit'];
}
// russian.json
{
serviceName: 'russian';
language: 'ru';
textDirection: 'ltr';
textLength: 'verbose';
socialMediaButtons: ['twitter', 'facebook', 'vk'];
}
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config/english.json
/russian.json
css/english.css
/russian.css
sass/english.scss
/russian.scss
/mixins/_textDirection.scss
/mixins/_textLength.scss
/mixins/_socialMediaButtons.scss
index.en.html
index.ru.html
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// english.scss
$english = true;
$script = 'latin';
// russian.scss
$russian = true;
$script = 'cyrillic';
@if $russian {
// apply styling only to Russian version
}
With a templating language, we can then plug data
from config files and hence customize HTML output
for every language.
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// english.scss
$english = true;
$script = 'latin';
$direction = 'left';
@include(mixins/directions);
@include(mainstyles);
// arabic.scss
$arabic = true;
$script = 'arabic';
$direction = 'right';
@include(mixins/directions);
@include(mainstyles);
@if $arabic {
// apply styling only to Arabic version
}
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// directions.scss
$margin-left: margin-left;
if $direction == 'right' {
$margin-left: margin-right;
}
$padding-left: padding-left;
if $direction == 'right' {
$padding-left: padding-right;
}
$left: left;
if $direction == 'right' {
$left: right;
}
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// directions.scss
$margin-left: margin-left;
if $direction == 'right' {
$margin-left: margin-right;
}
$padding-left: padding-left;
if $direction == 'right' {
$padding-left: padding-right;
}
$left: left;
if $direction == 'right' {
$left: right;
}
$margin-right: margin-right;
if $direction == 'right' {
$margin-right: margin-left;
}
$padding-right: padding-right;
if $direction == 'right' {
$padding-right: padding-left;
}
$right: right;
if $direction == 'right' {
$right: left;
}
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// global.scss
.nav-element {
#{$margin-left}: 10px;
#{$padding-right}: 10px;
#{$left}: 10px;
}
// english.css
.nav-element {
margin-left: 10px;
padding-right: 10px;
left: 10px;
}
// arabic.css
.nav-element {
margin-right: 10px;
padding-left: 10px;
right: 10px;
}
.nav-element {
float: flip(left, right);
padding: flip(10px 10px 0 0,
10px 0 0 10px);
line-height: get-script-value
(latin 1.3, arabic 1.6);
}
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// global.scss
.nav-element {
float: flip(left, right);
padding: flip(10px 10px 0 0, 10px 0 0 10px);
line-height: get-script-value(latin 1.3, arabic 1.6);
}
// english.css
.nav-element {
float: left;
padding: 10px 10px 0 0;
line-height: 1.3em;
}
// arabic.css
.nav-element {
float: right;
padding: 10px 0 0 10px;
line-height: 1.6em;
}
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Sometimes web fonts might be
out of question, so consider
generating full page screenshots
and sending a mix of HTML +
images to the users.
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“What if you want to use a full-
width element in a fixed-width
container? E.g. when you want
some content to extend beyond
the boundaries of the container?
— Tyler Sticka
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• HTML:
• CSS:
.u—containProse {
margin: 0 auto;
max-width: 40em;
}
...
...
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• HTML:
• CSS:
.u—containProse {
margin: 0 auto;
max-width: 40em;
}
...
...
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To release our child element from its
container, we need to know how much
space there is between the container
edge and the viewport edge.
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What’s this space exactly? Well, it’s
half the viewport width minus half the
container width. calc() to the rescue!
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• HTML:
• CSS:
.u—release {
margin-left: calc(-50vw + 50%);
margin-right: calc(-50vw + 50%);
}
...
...
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When the height or width of the
initial containing block is changed,
they are scaled accordingly. Note that
the initial containing block’s size is
affected by the presence of scrollbars
on the viewport.
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• HTML:
• CSS:
.u—release {
margin-left: calc(-50vw + 50%);
margin-right: calc(-50vw + 50%);
}
...
...
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• HTML:
• CSS:
.u—release {
margin-left: calc(-50vw + 50%);
margin-right: calc(-50vw + 50%);
}
html, body {
overflow-x: hidden;
}
...
...
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• CSS:
.u—release {
width: 100vw;
position: relative;
left: 50%;
right: 50%;
margin-left: -50vw;
margin-right: -50vw;
}
We push the container to the exact
middle of the browser window
with left: 50%, then pull it back to
the left edge with -50vw margin
(h/t Sven Wolfermann).
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“What if you want to build fluid
horizontal lines around centered
content for an art-directed
article? How exactly would you
build it?
— Jack Brewer
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• CSS:
.has-lines {
display: flex;
justify-content: center; // horizontal alignment
align-items: center; // replace stretch / v. alignment
}
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• CSS:
.has-lines {
display: flex;
justify-content: center; // horizontal alignment
align-items: center; // replace stretch / v. alignment
}
.has-lines:before, .has-lines:after {
content: '';
display: inline-block;
vertical-align: middle;
flex-grow: 1; // take all the space you can
height: 1px;
background: #ccc;
min-width: 20px;
}
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• CSS:
.has-lines {
display: flex;
justify-content: center; // horizontal alignment
align-items: center; // replace stretch / v. alignment
}
.has-lines:before, .has-lines:after {
content: '';
display: inline-block;
vertical-align: middle;
flex-grow: 1; // take all the space you can
height: 1px;
background: #ccc;
min-width: 20px;
}
.has-lines:before { margin-right: 20px; }
.has-lines:after { margin-left: 20px; }
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“So you want to implement a
baseline rhythm in CSS. Insert
two differently formatted
elements next to each other and
they’ll seem out of phase. How do
we bring them under control?
— Jan Dudek
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Often we define a common line height
value (or its multiple) that’s used for
all elements, including their paddings
and margins, occasionally taking
border widths into the equation.
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What if we align the baseline instead?
So that all type—regardless of its size
—lies on the same grid line? We just
need to calculate the offset and then
shift the content by that offset.
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By default, browsers center the cap
height between grid lines (the height
of a capital letter above the baseline).
So we shift it by half the difference
between line height and cap height.
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To determine the cap height, we
fiddle with offset values until the
type is properly aligned with the grid.
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$font-stacks: (
s: $font-stack-text,
m: $font-stack-text,
l: $font-stack-display,
xl: $font-stack-display
);
• vertical-rhythm.scss:
$line-height: 24px;
$font-sizes: (s: 13px, m: 15px, l: 19px, xl: 27px);
$cap-heights: (s: 0.8, m: 0.8, l: 0.68, xl: 0.68);
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$font-stacks: (
s: $font-stack-text,
m: $font-stack-text,
l: $font-stack-display,
xl: $font-stack-display
);
@function rhythm-shift($size-name) {
$font-size: map-get($font-sizes, $size-name);
$cap-height: map-get($cap-heights, $size-name);
$offset: ($line-height - $cap-height * $font-size) / 2;
return round($offset);
}
$line-height: 24px;
$font-sizes: (s: 13px, m: 15px, l: 19px, xl: 27px);
$cap-heights: (s: 0.8, m: 0.8, l: 0.68, xl: 0.68);
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Now we just need to apply the offset,
and do so reliably. We can combine
positive top margin and negative
bottom margin to make it work.
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.rhythm-m {
margin-top: $offset;
margin-bottom: -1 * $offset;
}
$offset: rhythm-shift(m);
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• Collapsing works differently with positive and
negative margins:
• Two positive margins
The bigger one wins.
• Two negative margins
The lower (i.e. the more negative) wins.
• One positive, one negative margin
The margins sum up.
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If an element doesn’t have a border
nor padding, and its first child has a
margin, that margin will flow out of
the parent. Use overflow: hidden.
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“What’s the best way to encode and
compress a 1×1px image? It could
be useful as a placeholder or
default image, for example.
— Jon Sneyers
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■
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Uncompressed pixel is just one bit to
four bytes – depending on how we
define it: as black & white (1 bit),
grayscale (1 byte), grayscale + alpha
(2 bytes), RGB (3 bytes), or RGBA
(4 bytes).
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Every image format specifies how to
interpret the data: the width and
height of the image, and the number
of bits or bytes per pixel (headers).
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• Image formats contain headers with some meta
information:
• Magic number
A fixed identifier, e.g. GIF87A/GIF89a, JFIF, Exif, PNG.
• Decoding details
Color profiles, orientation, gamma, or dots-per-pixel.
• Arbitrary metadata
Timestamps, copyright notices, or GPS coordinates.
• “Overhead” stuff
Markers and checksums or paddings for robustness.
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“What if you have to translate an
interface into many languages? The
length of words is unpredictable.
How do you manage it across
devices?
— Michael Scharnagl
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“Dealing with “above-the-fold” CSS
can be annoying — it has to be
maintained and can’t be cached
properly. Is there a better way?
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HTTP/1.1 Deployment Strategy
Deploying Critical CSS
• With HTTP/2, HTTP-requests are cheap.
Use the “scout” approach with many small files!
• Inlining critical CSS is an overhead in HTTP/2 world.
Server push is helpful but slow. Load CSS in series.
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HTTP/1.1 Deployment Strategy
Deploying Critical CSS
• Inlining critical CSS is an overhead in HTTP/2 world.
Server push is helpful but slow. Load CSS in series.
…content…
• We’ve moved away from…
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HTTP/1.1 Deployment Strategy
Deploying Critical CSS
• Inlining critical CSS is an overhead in HTTP/2 world.
Server push is helpful but slow. Load CSS in series.
/* Critical CSS styles */
• …towards:
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HTTP/1.1 Deployment Strategy
Deploying Critical CSS
/* Critical CSS styles, plus: */
article, .comments, aside, footer { display: none; }
loadCSS("full.css"); /* or rest.css + critical.css */
• …and then:
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HTTP/1.1 Deployment Strategy
Deploying Critical CSS
• A simple, “recommended” “HTTP/2” way:
…content…
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HTTP/1.1 Deployment Strategy
Deploying Critical CSS
• But “progressive CSS” way is even better:
…
…
…
…
…content…
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HTTP/1.1 Deployment Strategy
Deploying Critical CSS
• Multi-Stage CSS loading removes the need for
critical CSS, and provides sequential rendering.
• Browser behavior supports the technique;
browsers block rendering when necessary.
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“You’ve built a perfect grid with
perfectly sized thumbnail images
(e.g. squared size), but when the
client uploads images with
incorrect dimensions, they are
squished into the rectangle,
incorrectly resized. How do you
manage this issue?
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“For img src, we can use object-fit
property in CSS to “letterbox” the
images, preserving the ratio, or
crop the images inside the block.
For background images, we can
apply background-size exactly the
same way.
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“What if you wanted the color of the
SVG icon to inherit the color
property of a button in which it
resides? Can we use CSS alone
(no SASS/LESS) to establish this
relationship?
— Osvaldas Valutis
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“HTTP cache is unreliable. Is there
any way to keep assets such as
fonts, sprites or CSS/JS files in the
cache and improving performance
for subsequent visits in general?
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Service Workers: Foundation
• Service worker is a background process running JS.
It behaves like a proxy server on a user’s device.
• Websites register a service worker; it then intercepts all
network traffic between the site and the outside world.
• Once installed, browsers dispatch events to the service
worker first, for each network request.
• Goal: a reliable “native” proxy that would deliver
content when users are both online and offline.
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Offline Strategy
• Depending on complexity, we might use offline
caching, background processes, push notifications…
• A common offline strategy is quite simple:
— Explicitely cache resources like CSS, JS, fonts, images;
— Cache the homepage to display it when network fails;
— For other pages, have a “fallback” offline page.
• We need to register a Service worker first.
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Offline Strategy
• We need to register a Service worker first.
• JavaScript:
if (navigator.serviceWorker) {
navigator.serviceWorker.register(
'/sw.js', {
scope: '/'
});
}
• sw.js sits in the root to act on any request; otherwise it
acts on requests to a directory in which it resides.
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Offline Strategy
• JavaScript:
if (navigator.serviceWorker) {
navigator.serviceWorker.register(
'/sw.js', {
scope: '/'
});
}
• sw.js sits in the root to act on any request; otherwise it
acts on requests to a directory in which it resides.
• Caching of sw.js is capped for 24h via Cache-Control.
Browsers will review the file when accessing the site.
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Offline Strategy
• sw.js sits in the root to act on any request; otherwise it
acts on requests to a directory in which it resides.
• Next, we need to install the registered service worker.
self.addEventListener('install', function (event) {
event.waitUntil(updateStaticCache());
});
// Update 'version' if you need to refresh the cache
var staticCacheName='static';
var version='v1::';
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Offline Strategy
• Next, we need to install the registered service worker.
self.addEventListener('install', function (event) {
event.waitUntil(updateStaticCache());
});
// Update 'version' if you need to refresh the cache
var staticCacheName='static';
var version='v1::';
• By adding a version number (version), we can easily update
the cache later just by updating the version number.
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Offline Strategy
• We’ll populate cache with updateStaticCache().
// Store core files in a cache (incl. 'offline' page)
function updateStaticCache() {
return caches.open(version + staticCacheName)
.then(function (cache) {
return cache.addAll([
'js/scripts.js',
'css/styles.css',
'images/logo.svg',
'fonts/webfont.woff',
'/',
'/offline']);
});
};
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Offline Strategy
• Now we can activate the service worker. We’ll clean up
any outdated caches (checking the version number).
self.addEventListener('activate', function (event) {
event.waitUntil(
caches.keys()
.then(function (keys) {
// Remove caches whose name is no longer valid
return Promise.all(keys
.filter(function (key) {
return key.indexOf(version) !== 0; })
.map(function (key) {
return caches.delete(key); })
);
})
);
});
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Offline Strategy
• Register a service worker ✓
• Install a service worker ✓
• Versioning setup for a service worker ✓
• Cache population setup for a service worker ✓
• Activate a service worker ✓
• Managing cache for a service worker ✓
• Intercepting requests with a service worker.
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Offline Strategy
self.addEventListener('fetch', function (event) {
var request = event.request;
// Always fetch non-GET requests from network
if (request.method !== 'GET') {
event.respondWith(
fetch(request)
.catch(function () {
return caches.match('offline.html');
});
);
return;
}
• The fetch event is fired every time the browser is
going to request a file. We can intercept that request:
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Offline Strategy
• For HTML requests, try the network first. If it fails,
try to fetch cache. If all fails, show the offline page.
• For file requests, try to fetch files from cache first.
If it fails, make a network request. If it fails, use fallback.
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if (request.headers.get('Accept').indexOf('text/html') !== -1) {
event.respondWith(
fetch(request)
.then(function (response) {
// Put a copy of this page in the cache
var copy = response.clone();
caches.open(version + staticCacheName)
.then(function (cache) {
cache.put(request, copy);
});
return response;
})
.catch(function () {
return caches.match(request)
.then(function (response) {
return response || caches.match('/offline.html');
})
})
);
return;
}
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if (request.headers.get('Accept').indexOf('text/html') !== -1) {
event.respondWith(
fetch(request)
.then(function (response) {
// Put a copy of this page in the cache
var copy = response.clone();
caches.open(version + staticCacheName)
.then(function (cache) {
cache.put(request, copy);
});
return response;
})
.catch(function () {
return caches.match(request)
.then(function (response) {
return response || caches.match('/offline.html');
})
})
);
return;
}
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Offline Strategy
• For HTML requests, try the network first. If it fails,
try to fetch cache. If all fails, show the offline page.
• For file requests, try to fetch files from cache first.
If it fails, make a network request. If it fails, use fallback.
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// For non-HTML, try cache first, then fall back to the network
event.respondWith(
caches.match(request)
.then(function (response) {
return response || fetch(request)
.catch(function () {
// If request is img, show offline placeholder
if (request.headers.get('Accept').
indexOf('image') !== -1) {
return new Response(
'', { headers: { 'Content-
Type': 'image/svg+xml' }}
);
}
});
})
);
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Offline Strategy
• Register a service worker ✓
• Install a service worker ✓
• Versioning setup for a service worker ✓
• Cache population setup for a service worker ✓
• Activate a service worker ✓
• Managing cache for a service worker ✓
• Intercepting requests with a service worker ✓
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Service Workers Gotchas
• Service workers require a secure connection
(HTTPS) and are based on ES6 Promises.
• Cache API is completely separate from HTTP cache.
Response is a stream; to cache it, you need to copy it first.
• A service worker can have multiple caches and can be
registered many times; the browser will figure it out.
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Service Workers Gotchas
• If a service worker is broken, browsers will
skip the code and fall back to the network.
• Service workers use only asynchronous APIs.
E.g. they can’t work with localStorage (synchronous).
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“Is there any way to isolate
expensive components, similar to
lazy loading, and paint important
content faster using CSS alone?
— Michael Scharnagl
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The contain property is a primitive
for isolating style, layout and paint.
It allows us to limit a specific DOM
sub-tree and the rest of the
document with native boundaries.
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• With the contain property, we can define priorities
for loading and painting CSS components.
• Third-party widgets
Delay expensive layout with contain: strict.
• Off-screen modules
Delay expensive paints with contain: paint.
• Container queries
Focus on the local scope with contain: strict.
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• With the contain property, we can define priorities
for loading and painting CSS components.
• Third-party widgets
Delay expensive layout with contain: strict.
• Off-screen modules
Delay expensive paints with contain: paint.
• Container queries
Focus on the local scope with contain: strict.
• Browser support is coming.
Enabled by default in Chrome 52.
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“When using web fonts, we want
users to be able to access the
content as fast as possible, yet also
avoid irritating repaints and reflows
in the browser. What would be the
best font loading strategy today?
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Web Fonts Dilemma
• The choice of formats depends on browser support:
• WOFF (Web Open Font Format)
• TTF (TrueType)
• OTF (OpenType)
• EOT (Embedded OpenType)
• SVG Fonts (Scalable Vector Graphics)
• WOFF2 (Web Open Font Format 2)
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Web Fonts Dilemma
• WOFF2 has the best compression, but isn’t
supported by older Android/iOS. WOFF is.
• Old Android and iOS support TTF and OTF;
Internet Explorer 6–8 needs EOT.
• SVG doesn’t support OpenType features.
Not supported in IE, Chrome or Firefox.
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Web Fonts Dilemma
• WOFF2 has the best compression, but isn’t
supported by older Android/iOS. WOFF is.
• Old Android and iOS support TTF and OTF;
Internet Explorer 6–8 needs EOT.
• SVG doesn’t support OpenType features.
Supported in Chrome, Safari, Opera.
• Strategy: WOFF/2 with TTF/OTF and EOT for
IE 6–8; not SVG. Best compression always wins.
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Declaring @font-face
• We can use bulletproof @font-face syntax to
avoid common traps along the way:
• CSS:
@font-face {
font-family: 'Elena Regular';
src: url('elena.eot?#iefix') format('embedded-opentype'),
url('elena.woff2') format('woff2'),
url('elena.woff') format('woff'),
url('elena.otf') format('opentype');
}
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Declaring @font-face
• If you want only smart browsers (IE9+) to
download fonts, declaration can be shorter:
• CSS:
@font-face {
font-family: 'Elena Regular';
src: url('elena.woff2') format('woff2'),
url('elena.woff') format('woff'),
url('elena.otf') format('opentype');
}
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• CSS:
@font-face {
font-family: 'Elena Regular';
src: url('elena.woff2') format('woff2'),
url('elena.woff') format('woff'),
url('elena.otf') format('opentype');
}
• When a font family name is used in CSS,
browsers match it against all @font-face
rules, download web fonts, display content.
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• When a font family name is used in CSS,
browsers match it against all @font-face
rules, download web fonts, display content.
• CSS:
body {
font-family: 'Skolar Regular',
AvenirNext, Avenir, /* iOS */
'Roboto Slab', 'Droid Serif', /* Android */
'Segoe UI', /* Microsoft */
Georgia, 'Times New Roman', serif; /* Fallback */
}
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• CSS:
body {
font-family: 'Skolar Regular',
AvenirNext, Avenir, /* iOS */
'Roboto Slab', 'Droid Serif', /* Android */
'Segoe UI', /* Microsoft */
Georgia, 'Times New Roman', serif; /* Fallback */
}
• HTML:
try{Typekit.load();}catch(e){}
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• Once DOM and CSSOM are constructed, if
@font-face matches, a font will be required.
• If fonts aren’t cached yet, they will be requested,
downloaded and applied, deferring rendering.
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• FOUT (Flash Of Unstyled Text): show content in
fallback fonts first, then switch to web fonts.
• FOIT (Flash Of Invisible Text): no content
displayed until the font becomes available.
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CSS Font Loading API
• Native browser API à la Web Font Loader, with a
FontFace object representing @font-face rules.
• JavaScript:
var elena_reg = new FontFace(
'Elena Regular',
'url(elena_reg.woff) format("woff"),' +
'url(elena_reg.otf) format("otf")',
{ weight: 'regular', unicodeRange: 'U+0-7ff' }
);
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• JavaScript:
document.fonts.load('1em elena_reg')
.then(function() {
var docEl = document.documentElement;
docEl.className += ' fonts-ready‘;
}).catch(function () {
var docEl = document.documentElement;
docEl.className += ' fonts-failed';
});
• JavaScript:
var elena_reg = new FontFace(
'Elena Regular',
'url(elena_reg.woff) format("woff"),' +
'url(elena_reg.otf) format("otf")',
{ weight: 'regular', unicodeRange: 'U+0-7ff' }
);
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• JavaScript:
document.fonts.load('1em elena_reg')
.then(function() {
var docEl = document.documentElement;
docEl.className += ' fonts-ready‘;
}).catch(function () {
var docEl = document.documentElement;
docEl.className += ' fonts-failed';
});
• CSS:
.fonts-loaded h1 {
font-family: "Elena Regular";
}
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• JavaScript:
document.fonts.load('1em elena_reg’)
.then(function() {
var docEl = document.documentElement;
docEl.className += ' fonts-ready’;
}).catch(function () {
var docEl = document.documentElement;
docEl.className += ' fonts-failed’;
});
• CSS:
.fonts-loaded h1 {
font-family: "Elena Regular";
font-rendering: "block 0s swap infinite"; // FOUT
// font-rendering: "block 3s swap infinite"; // FOIT
}
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• JavaScript:
document.fonts.load('1em elena_reg’)
.then(function() {
var docEl = document.documentElement;
docEl.className += ' fonts-ready’;
}).catch(function () {
var docEl = document.documentElement;
docEl.className += ' fonts-failed’;
});
• CSS:
.fonts-loaded h1 {
font-family: "Elena Regular";
// font-rendering: "block 0s swap infinite"; // FOUT
font-rendering: "block 3s swap 3s"; // FOIT, at most 3sec
}
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“What if you have a large photo that
requires a transparent shadow?
PNG is too large in file size, and
JPEG isn’t good enough in quality.
Trick: create a regular non-
transparent JPG and an 8-bit PNG
(alpha mask) and load both images
inside an SVG container.
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• HTML/CSS:
, background: url("hero-image.svg")
![]()
![]()
• hero-image.svg:
, background: url("hero-image.svg")
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“How do you efficiently scale up /
down any UI component (e.g. a
slider or calendar) and keep all
the proportions intact—without
fiddling with width, height or
border-radius manually?
— @simurai
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“By sneaking a Trojan horse into
your components. We use rem for
components “root” and em for sub-
parts of the components. Then, by
adjusting the font-size of the root,
we adjust all size-related CSS
properties of a component at once.
— @simurai
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“What if you wanted to style a block
with a light background color
differently than if the same block
has a dark background image? Or
reverse text color based on bg color
automatically in CSS?
— Osvaldas Valutis
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“The mix-blend-mode property
defines how an element’s content
should blend with its background.
Use mix-blend-mode: difference or
mix-blend-mode: darken to have
backgrounds, shapes, and text all
interact in subtle/interesting ways.
— Robin Rundle
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• CSS:
.letterbox { background-color: #fff; }
.letterbox-letter { fill: #f7ff33;
mix-blend-mode: darken;
/* The background is replaced with the color that is
darker, otherwise it is left as it was. */ }
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“What if you want all links to have
an underline except the ones you
specify? Or you want all ’s in the
navigation to have a right border,
except the last one. Normally you
would use :last-child (or extra class)
to overwrite a default CSS rule.
— Ire Aderinokun
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“You’ve built an alert message box.
To be resilient to failure, how can
we make sure that the box will be
hidden when there is no content
within it?
— Ire Aderinokun
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“Mobile browsers will wait approx.
300ms from the time that you tap
the button to fire the click event.
The reason for this is that the
browser is waiting to see if you are
actually performing a double tap.
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The touch-action property in CSS
can be used to disable this
behaviour. With touch-action:
manipulation, the user agent may
consider touches that begin on the
element only for the purposes of
scrolling and continuous zooming.
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“What if you have 3 containers
(thumbnails gallery), each 33%
width, but they also have padding
defined in em values, and border
defined in px values? The layout
might break because width doesn’t
consider those values.
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“We can apply the good ol’ IE Box
Model to ensure that whenever we
define width (or height), it always
includes the padding and the
border as well. We do that by
applying box-sizing: border-box to
pretty much everything.
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“What if you want to create some
sort of visual distortion? E.g. for
headlines or hero banners or
prominent boxes. Can we achieve
it with CSS/HTML alone?
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“There are many little details that
often make an experience just
annoying. E.g. an age prompt once
you try to access an age-restricted
website. Can we do better?
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• Email verification is unnecessary
60% of users consistently copy/paste their email
when asked to verify it in the checkout.
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• Email verification is unnecessary
Remove the email verification field altogether, or
use inline autocomplete or “review” page instead.
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Summary
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Summary
— apply pseudo-elements on broken images
— contain: strict reduces painting costs
— fluid type with font-size: calc (1em + 1vw)
— nested links with
— highlight row/column with pseudo-elements
— control table-layout with table-layout: fixed
— padded lines with the box-shadow trick
— consider critical progressive CSS (HTTP/2)
— use object-fit: cover to letterbox images
— use native variables with CSS currentColor
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Summary
— service workers can boost performance a lot
— test scan levels to improve image delivery
— early fetch of critical resources with preload
— add interface screens to pattern libraries
— use the Font Loading API to load web fonts
— replace age prompt with a year prompt
— replace country selector with autosuggest
— replace email verification with email review
— load maps/lightboxes conditionally
— experiment and produce something creative.
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Thank you.
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Image credits
• Front cover: Geometric Wallpapers
by Simon C Page (http://simoncpage.co.uk/
blog/2012/03/ipad-hd-retina-wallpaper/)
• Sections illustrations: “bisous les copains”,
by Guillaume Kurkdjian (http://
bisouslescopains.tumblr.com/)
• Techniques: by (tremendous) web design
community.