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∞ things I didn’t know
about HTML, CSS &
JavaScript
@mathias · #arrrrcamp
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@mathias
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Back to the ’90s
kickin’ it old skool
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Background colors
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Background colors
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Background colors
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Background colors
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Background colors
!
#FF33FF
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Background colors
!
#0F030F
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Background colors
!
#00C000
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Background colors
!
#000000
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Background colors
!
#C00000
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Background colors
!
#C0A000
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Background colors
!
#000000
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Background colors
! #A000A0
http://mths.be/bpf
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“Valid HTML”
conformance criteria
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Document Type Definition
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DTD
Lorem ipsum.
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DTD
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DTD fail
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DTD fail
foo
bar
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DTD fail
→ can still be checked by a computer
foo
bar
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Computer says no
not a quote
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Computer says no
→ can only be checked by a human
→ can only be checked by a human
not a quote
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Take-away
Don’t obsess about HTML validation.
• not the whole story
• validators have bugs, too
Functionality trumps validation anyway.
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Character references
aka. “entities”
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Character references
foo & bar
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;
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github:twbs/bootstrap#3057
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;
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;
PRETENDS TO BE OPTIONAL
BREAKS STUFF WHEN OMITTED
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Character references
foo & bar
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Character references
foo & bar
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Character references
foo&bar
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Character references
foo & bar
http://mths.be/bduSlide 36
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Character references
foo > bar
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Character references
foo > bar
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Character references
foo>bar
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Character references
foo > bar
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Tags
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Valid HTML
Foo
…
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Valid HTML
Foo
…
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Valid HTML
Huh?
…
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Valid HTML
Huh?
…
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Valid HTML
lolwut
…
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No content
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No content
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^
n
FTFY
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Using CSS without
HTML
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No content
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No content
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Attribute values
$ curl -i http://mathiasbynens.be/demo/css-without-html
HTTP/1.1 200 OK
Date: Wed, 03 Oct 2013 13:33:37 GMT
Link: ;rel=stylesheet
Content-Length: 0
Content-Type: text/html; charset=UTF-8
http://mths.be/bpe
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No content
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Font family names
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CSS
html {
font-family: 'Comic Sans MS';
}
“If there’s whitespace in the font family name,
it must be quoted.”
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CSS
html {
font-family: Comic Sans MS;
}
“If there’s whitespace in the font family name,
it must be quoted.”
http://mths.be/bft
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CSS
html {
font-family: 456bereastreet;
}
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CSS
html {
font-family: 456bereastreet;
}
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CSS
html {
font-family: \34 56bereastreet;
}
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CSS
html {
font-family: \34 56bereastreet;
}
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CSS
html {
font-family: '456bereastreet';
}
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CSS
http://mths.be/bjm
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Attribute values
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Attribute values
…
a[href="foo|bar"] {
background: hotpink;
}
http://mths.be/bal
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Attribute values
http://mths.be/bjn
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Characters in JS
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JavaScript string length
>> 'A'.length // U+0041
1
>> 'A' == '\u0041'
true
>> 'B'.length // U+0042
1
>> 'B' == '\u0042'
true
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String length ≠ char count
>> 'A'.length // U+1D400
2
>> 'A' == '\uD835\uDC00'
true
>> 'B'.length // U+1D401
2
>> 'B' == '\uD835\uDC01'
true
http://mths.be/bed
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Surrogate pairs
// for non-BMP code points (> 0xFFFF)
function getSurrogates(codePoint) {
var high = Math.floor((codePoint - 0x10000) / 0x400) + 0xD800;
var low = (codePoint - 0x10000) % 0x400 + 0xDC00;
return [ high, low ];
}
function getCodePoint(high, low) {
var codePoint = (high - 0xD800) * 0x400 + low - 0xDC00 + 0x10000;
return codePoint;
}
>> getSurrogates('A'); // U+1D400
[ 0xD835, 0xDC00 ]
>> getCodePoint(0xD835, 0xDC00);
0x1D400
http://mths.be/bed
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JS string character count
function countSymbols(string) {
return punycode.ucs2.decode(string).length;
}
>> countSymbols('A') // U+0041
1
>> countSymbols('A') // U+1D400
1
http://mths.be/punycode
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JS variable names
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Which is invalid?
var H
̹̙̦̮͉̩̗̗ͧ̇̏̊̾
E
ͨ͆͒̆ͮ̃͏̷̮̣̫̤̣
C
ͯ̂͐͏̨̛͔̦̟͈̻
O
̜͎͍͙͚̬̝̣̽ͮ͐͗̀ͤ̍̀͢
M
̴̡̲̭͍͇̼̟̯̦̉̒͠Ḛ̛̙̞̪̗ͥͤͩ̾͑̔͐ͅṮ̴̷̷̗̼͍̿̿̓̽͐
H
̙̙̔̄͜
;
var !_ಠӹಠ_!;
var ϗ_₹îਓ
Ǝ
ℵೋ⏺
Δ
େ;
var
ʃː
λ
ˀπ
ᐩᐨᐟᑉᐦᐸᐳƘƖ\u200C;
var a;
http://mths.be/ber
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♥ JS
var H
̹̙̦̮͉̩̗̗ͧ̇̏̊̾
E
ͨ͆͒̆ͮ̃͏̷̮̣̫̤̣
C
ͯ̂͐͏̨̛͔̦̟͈̻
O
̜͎͍͙͚̬̝̣̽ͮ͐͗̀ͤ̍̀͢
M
̴̡̲̭͍͇̼̟̯̦̉̒͠Ḛ̛̙̞̪̗ͥͤͩ̾͑̔͐ͅṮ̴̷̷̗̼͍̿̿̓̽͐
H
̙̙̔̄͜
; // valid
var !_ಠӹಠ_!; // valid
var ϗ_₹îਓ
Ǝ
ℵೋ⏺
Δ
େ; // valid
var
ʃː
λ
ˀπ
ᐩᐨᐟᑉᐦᐸᐳƘƖ\u200C; // valid
var a; // syntax error
http://mths.be/ber
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/^(?!(?:do|if|in|for|let|new|try|var|case|else|
enum|eval|false|null|this|true|void|with|break|
catch|class|const|super|throw|while|yield|delete|
export|import|public|return|static|switch|typeof|
default|extends|finally|package|private|continue|
debugger|function|arguments|interface|protected|
implements|instanceof)$)[$A-Z\_a-z\xaa\xb5\xba
\xc0-\xd6\xd8-\xf6\xf8-\u02c1\u02c6-\u02d1\u02e0-
\u02e4\u02ec\u02ee\u0370-
\u0374\u0376\u0377\u037a-\u037d\u0386\u0388-
\u038a\u038c\u038e-\u03a1\u03a3-\u03f5\u03f7-
\u0481\u048a-\u0527\u0531-\u0556\u0559\u0561-
\u0587\u05d0-\u05ea\u05f0-\u05f2\u0620-\u064a
http://mths.be/bpg
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\u203f\u2040\u2054\u20d0-\u20dc\u20e1\u20e5-
\u20f0\u2cef-\u2cf1\u2d7f\u2de0-\u2dff\u302a-
\u302f\u3099\u309a\ua620-\ua629\ua66f\ua674-
\ua67d\ua69f\ua6f0\ua6f1\ua802\ua806\ua80b\ua823-
\ua827\ua880\ua881\ua8b4-\ua8c4\ua8d0-
\ua8d9\ua8e0-\ua8f1\ua900-\ua909\ua926-\ua92d
\ua947-\ua953\ua980-\ua983\ua9b3-\ua9c0\ua9d0-
\ua9d9\uaa29-\uaa36\uaa43\uaa4c\uaa4d\uaa50-
\uaa59\uaa7b\uaab0\uaab2-\uaab4\uaab7\uaab8\uaabe
\uaabf\uaac1\uaaeb-\uaaef\uaaf5\uaaf6\uabe3-
\uabea\uabec\uabed\uabf0-\uabf9\ufb1e\ufe00-
\ufe0f\ufe20-\ufe26\ufe33\ufe34\ufe4d-\ufe4f
\uff10-\uff19\uff3f]*$/
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JS variable names
http://mths.be/bjo
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Truthiness in JS
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JavaScript
if (condition) {
log('`condition` is truthy');
} else {
log('`condition` is falsy');
}
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ToBoolean(condition)
Argument type Result
undefined false
null false
boolean same as input
number +0, -0, NaN → false
otherwise → true
string empty string → false
otherwise → true
object true
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>> document.all
[object HTMLCollection]
>> !!document.all
false
“All objects are truthy”
except in the DOM…
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if (document.all) {
// code that uses `document.all`,
// for ancient browsers
} else if (document.getElementById) {
// code that uses `document.getElementById`,
// for “modern” browsers
}
But… Why?
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Benchmarking
JavaScript timers
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JavaScript
var totalTime,
start = new Date,
iterations = 6;
while (iterations--) {
// Code snippet goes here
}
// totalTime
!
the number of milliseconds it took
// to execute the code snippet 6 times
totalTime = new Date - start;
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JavaScript
var hz,
period,
startTime = new Date,
runs = 0;
do {
// Code snippet goes here
runs++;
totalTime = new Date - startTime;
} while (totalTime < 1000);
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JavaScript
// convert ms to seconds
totalTime /= 1000;
// period
!
how long per operation
period = totalTime / runs;
// hz
!
the number of operations per second
hz = 1 / period;
// can be shortened to
// hz = (runs * 1000) / totalTime;
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JavaScript
“When Windows XP boots, the typical default clock
interrupt period is 10 milliseconds, although a
period of 15 milliseconds is used on some systems.
That means that every 10 milliseconds, the
operating system receives an interrupt from the
system timer hardware.”
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JavaScript
“When Windows XP boots, the typical default clock
interrupt period is 10 milliseconds, although a
period of 15 milliseconds is used on some systems.
That means that every 10 milliseconds, the
operating system receives an interrupt from the
system timer hardware.”
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Benchmark.js
• Detects various timers
• (new Date).getTime() (ms)
• chrome.Interval (µs)
• performance.now (µs)
• Node microtime module (µs)
• Node’s high-res timer (ns)
• Java timer applet (ns)
• Performs statistical analysis of results
• Used in RoboHornet and on jsPerf.com
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jsPerf.com
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Questions?
@mathias