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@stefanjudis I didn't know that!

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My first job interview

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“ We're running a Magento shop combined with a CouchDB and a Frontend application with a Prototype/ jQuery mix.

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“ We're running a Magento shop combined with a CouchDB and a Frontend application with a Prototype/ jQuery mix.

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“ We're running a Magento shop combined with a CouchDB and a Frontend application with a Prototype/ jQuery mix.

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“ We're running a Magento shop combined with a CouchDB and a Frontend application with a Prototype/ jQuery mix. I didn't say that I didn't know most of these technologies...

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... which lead to enormous stress.

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8 years later

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The dangerous knowledge comparison

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What I think others know What I know

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Web Development

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You can't know everything!

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“ Don’t Compare Your Behind-The-Scenes With Everyone's Highlight Reel. by Tara Hunt

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Know where to look for information

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The learning journey 
 won't end.

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TIL: ... (Today I learned: ...)

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But then I learned it's deprecated...

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Twitter is neither a bookmarking nor documentation tool!

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Write it down! Quick'n'dirty!

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My learnings in 2 years (a random list in no particular order) (not always useful)

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NaNNaNNaN NaNNaN

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parseInt('Hello world', 10)

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parseInt('Hello world', 10) NaN

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parseInt('Hello world', 10) NaN === NaN false

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isNaN(NaN); // true

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isNaN(NaN); // true isNaN(undefined); // true isNaN({}); // true isNaN(true); // false isNaN(null); // false isNaN(37); // false

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isNaN(NaN); // true isNaN(undefined); // true isNaN({}); // true isNaN(true); // false isNaN(null); // false isNaN(37); // false function myIsNaN(value) { return value !== value; }

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isNaN(NaN); // true isNaN(undefined); // true isNaN({}); // true isNaN(true); // false isNaN(null); // false isNaN(37); // false myIsNaN(NaN); // true myIsNaN(undefined); // false myIsNaN({}); // false myIsNaN(true); // false myIsNaN(null); // false myIsNaN(37); // false

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isNaN(NaN); // true isNaN(undefined); // true isNaN({}); // true isNaN(true); // false isNaN(null); // false isNaN(37); // false myIsNaN(NaN); // true myIsNaN(undefined); // false myIsNaN({}); // false myIsNaN(true); // false myIsNaN(null); // false myIsNaN(37); // false Number.isNaN(NaN); // true Number.isNaN(undefined); // false Number.isNaN({}); // false Number.isNaN(true); // false Number.isNaN(null); // false Number.isNaN(37); // false

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isNaN(NaN); // true isNaN(undefined); // true isNaN({}); // true isNaN(true); // false isNaN(null); // false isNaN(37); // false myIsNaN(NaN); // true myIsNaN(undefined); // false myIsNaN({}); // false myIsNaN(true); // false myIsNaN(null); // false myIsNaN(37); // false Number.isNaN(NaN); // true Number.isNaN(undefined); // false Number.isNaN({}); // false Number.isNaN(true); // false Number.isNaN(null); // false Number.isNaN(37); // false Object.is(NaN, NaN); // true Object.is(undefined, NaN); // false Object.is({}, NaN); // false Object.is(true, NaN); // false Object.is(null, NaN); // false Object.is(37, NaN); // false

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Object.is? === + SPECIAL HANDLING OF NaN, -0, +0

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Object.is? Object.is(-0, 0); // false Object.is(NaN, NaN); // true SameValue Comparison

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['foo', 123, true, undefined, NaN].indexOf(NaN) ['foo', 123, true, undefined, NaN].includes(NaN) true ['foo', 123, true, undefined, -0].includes(0) true SameValueZero Comparison -1

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Abstract Equality Comparison Equality comparison and sameness == Strict Equality Comparison ===, indexOf, ... SameValueZero includes, ... SameValue Object.is, ...

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developer.mozilla.org/en-US/docs/Web/JavaScript/Equality_comparisons_and_sameness

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Should I (force) push it?

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$ history | grep amend 53 git co -p --amend index.html 69 git co -p --amend 71 git co -p --amend content/blueprints 1538 git co -p --amend 1540 git co -p --amend migration-tests 1542 git co -p --amend migration-tests 1545 git co -p --amend test_app.py 1627 git co -p --amend 1842 git co --amend 1845 git co --amend 1941 git co --amend 2273 git co -p --amend ...

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$ git co -p --amend index.html $ git push -f origin some-feature

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$ git co -p --amend index.html $ git push -f origin some-feature It's very easy to overwrite remote changes with force pushing!

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developer.atlassian.com/blog/2015/04/force-with-lease/

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Process substitution

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Process substitution $ bash <(curl -s https://codecov.io/bash)

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“ Process substitution allows a process’s input or output to be referred to using a filename.

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$ echo <(ls .) /dev/fd/11

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$ cat <(ls .) functions.sh .zshrc ...

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$ node <(echo 'console.log("foo")') foo

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$ node <(pbpaste) foo

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$ node <(pbpaste) foo console.log("foo") But then I learned you can pipe into Node.js

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$ node <(pbpaste) foo

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$ pbpaste | node foo

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Break zooming with one line

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body { font-size: 2vw; }

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body { font-size: calc(1vw + 1em); }

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Stylesheets do not only block rendering

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app.css START RENDER

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var script = document.createElement('script'); script.src = "analytics.js"; document.getElementsByTagName('head')[0].appendChild(script);

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var script = document.createElement('script'); script.src = "analytics.js"; document.getElementsByTagName('head')[0].appendChild(script); app.css analytics.js

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var script = document.createElement('script'); script.src = "analytics.js"; document.getElementsByTagName('head')[0].appendChild(script); 
 
 app.css analytics.js

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WAT!!!

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{ 'ü': 'foo', 'ü': 'bar', '': 'baz', '': 'wat!' }

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{ 'ü': 'foo', 'u\u0308': 'bar', '': 'baz', '': 'wat!' }

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{ 'ü': 'foo', 'u\u0308': 'bar', '': 'baz', '\uD83D\uDC68\u200D\uD83D\uDC69\u200D\uD83D\uDC66': 'wat!' }

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“ Two IdentifierName that are canonically equivalent according to the Unicode standard are not equal unless they are represented by the exact same sequence of code units.

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“ Two IdentifierName that are canonically equivalent according to the Unicode standard are not equal unless they are represented by the exact same sequence of code units.

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Unicode is powerful and very fascinating (and scary)

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https://www.fileformat.info/info/unicode/char/202e/index.htm

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"Logical" string comparisons

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'aBcD' === 'abcd'

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'aBcD' === 'abcd' // false

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'aBcD' === 'abcd' // false 'ábcd' === 'abcd'

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'aBcD' === 'abcd' // false 'ábcd' === 'abcd' // false

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'aBcD' === 'abcd' // false 'ábcd' === 'abcd' // false 'Price 2€' > 'Price 1€'

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'aBcD' === 'abcd' // false 'ábcd' === 'abcd' // false 'Price 2€' > 'Price 1€' // true

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'aBcD' === 'abcd' // false 'ábcd' === 'abcd' // false 'Price 2€' > 'Price 1€' // true 'Price 20€' > 'Price 3€'

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'aBcD' === 'abcd' // false 'ábcd' === 'abcd' // false 'Price 2€' > 'Price 1€' // true 'Price 20€' > 'Price 3€' // false

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localCompare 'aBcD'.localeCompare('abcd', undefined, { sensitivity: 'base' }) // 0 'ábcd'.localeCompare('abcd', undefined, { sensitivity: 'base' }) // 0

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localCompare a ≠ b, a = á, a = A 'aBcD'.localeCompare('abcd', undefined, { sensitivity: 'base' }) // 0 'ábcd'.localeCompare('abcd', undefined, { sensitivity: 'base' }) // 0

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localCompare 'Price 2€'.localeCompare('Price 3€', undefined, { numeric: true }) // -1 'Price 3€'.localeCompare('Price 3€', undefined, { numeric: true }) // 0 'Price 23€'.localeCompare('Price 3€', undefined, { numeric: true }) // 1

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localCompare 'Price 2€'.localeCompare('Price 3€', undefined, { numeric: true }) // -1 'Price 3€'.localeCompare('Price 3€', undefined, { numeric: true }) // 0 'Price 23€'.localeCompare('Price 3€', undefined, { numeric: true }) // 1 "1" < "2" < "10"

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How to center elements

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.center { display: flex; align-items: center; justify-content: center; }

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.center { display: flex; align-items: center; justify-content: center; } .center-using-grid { display: grid; align-items: center; justify-items: center; }

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.center { display: flex; align-items: center; justify-content: center; } .center-using-grid { display: grid; place-items: center; }

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.center { display: flex; align-items: center; justify-content: center; } .center-using-grid { display: grid; place-items: center; } 2 declarations!

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developer.mozilla.org/en-US/docs/Web/CSS/place-items place-items support

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Querying the DOM is not equal querying the DOM

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  • foo
  • bar
  • baz
document.querySelectorAll('li'); // NodeList(3) [li, li, li]

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  • foo
  • bar
  • baz
document.querySelectorAll('li'); // NodeList(3) [li, li, li] document.getElementsByTagName('li'); // HTMLCollection(3) [li, li, li]

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  • foo
  • bar
  • baz
NodeList(3) HTMLCollection(3)

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  • foo
  • bar
  • baz
  • wat
NodeList(3) HTMLCollection(4)

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  • foo
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  • baz
  • wat
NodeList(3) HTMLCollection(4) There are live and static element collections

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document.querySelectorAll // static NodeList

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document.querySelectorAll // static NodeList element.childNodes // live NodeList

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document.querySelectorAll // static NodeList element.childNodes // live NodeList element.children // (live) HTMLCollection

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document.querySelectorAll // static NodeList element.childNodes // live NodeList element.children // (live) HTMLCollection document.getElementsByTagName // (live) HTMLCollection

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www.stefanjudis.com/blog/accessing-the-dom-is-not-equal-accessing-the-dom

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WAT!!! (part 2)

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Fooo

Some more information

#foo:hover { background: DeepSkyBlue; }

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“ Document languages may define additional ways in which an element can match :hover. For example, [HTML5] defines a labeled control element as matching :hover when its label is hovered.

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“ Document languages may define additional ways in which an element can match :hover. For example, [HTML5] defines a labeled control element as matching :hover when its label is hovered.

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kizu.ru/en/blog/label-to-input/

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Regular expressions

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const regex = /Jane.Smith/; regex.test('Jane Smith'); // true regex.test('Jane\nSmith'); // false

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const regex = /Jane.Smith/; regex.test('Jane Smith'); // true regex.test('Jane\nSmith'); // false '.' doesn't actually match all characters!

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const regex = /Jane.Smith/; regex.test('Jane Smith'); // true regex.test('Jane\nSmith'); // false

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const regex = /Jane.Smith/s; regex.test('Jane Smith'); // true regex.test('Jane\nSmith'); // true

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github.com/tc39/proposal-regexp-dotall-flag

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* * use with Babel dotall flag support * *

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const regex = /Jane.Smith/;

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const regex = /(Jane|John).(Smith|Miller)/; 'John Smith'.match(regex); // [ "John Smith", "John", "Smith" ]

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const regex = /(Jane|John).(Smith|Miller)/; 'John Smith'.match(regex); // [ "John Smith", "John", "Smith" ]

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const regex = /(?:Jane|John).(Smith|Miller)/; 'John Smith'.match(regex); // [ "John Smith","Smith" ]

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const regex = /(?:Jane|John).(Smith|Miller)/; 'John Smith'.match(regex); // [ "John Smith","Smith" ] There are non-capturing groups in JavaScript

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Why we won't have element queries

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Why we (probably) won't have element queries

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.mod img { display: block; margin: 0 auto; width: 100%; max-width: 250px; }

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.mod img { display: block; margin: 0 auto; width: 100%; max-width: 250px; } .mod:media( min-width: 425px ) img { float: left; width: 30%; max-width: 9999px; }

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.box { width: 1200px; }

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.box { width: 1200px; }

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.box { width: 1200px; } .box:media(min-width: 1200px) { width: 1000px; }

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.box { width: 1200px; } .box:media(min-width: 1200px) { width: 1000px; }

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.box { width: 1200px; } .box:media(min-width: 1200px) { width: 1000px; }

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.box { width: 1200px; } .box:media(min-width: 1200px) { width: 1000px; }

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.box { width: 1200px; } .box:media(min-width: 1200px) { width: 1000px; }

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.box { width: 1200px; } .box:media(min-width: 1200px) { width: 1000px; } And now, we're in a loop...

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https://css-tricks.com/selectors-that-depend-on-layout/

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Checking for an existing class

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const elem = querySelector('.component'); if( elem.classList.contains('is-active') && elem.classList.contains('is-awesome') ) { /* ... */ }

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const elem = querySelector('.component'); if( elem.matches('.is-active') && elem.matches('.is-awesome') ) { /* ... */ }

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const elem = querySelector('.component'); if(elem.matches('.is-active.is-awesome')) { /* ... */ }

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“ The Element.matches() method returns true if the element would be selected by the specified selector string; otherwise, returns false.

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“ The Element.matches() method returns true if the element would be selected by the specified selector string; otherwise, returns false.

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background-repeat has other options than repeat

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.box { }

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.box { background-image: url(https://.../jsunconf.svg); }

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.box { background-image: url(https://.../jsunconf.svg); background-repeat: repeat; }

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.box { background-image: url(https://.../jsunconf.svg); background-repeat: round; }

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.box { background-image: url(https://.../jsunconf.svg); background-repeat: space; }

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min-content/ max-content

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Merel van der Woude Creative director bij Butterfly Works

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Merel van der Woude Creative director

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Merel van der Woude Creative director, overall great person, loves books

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Merel van der Woude Creative director, overall great person, loves books

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Merel van der Woude Creative director, overall great person, loves books That's not possible, is it?

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Merel van der Woude Creative director

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Merel van der Woude Creative director

h2 { width: min-content; min-width: 0; max-width: 100%; }

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Merel van der Woude Creative director

h2 { width: min-content; min-width: 0; max-width: 100%; } h2 span { width: max-content; max-width: 100%; }

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https://codepen.io/maddesigns/pen/YNXvMz

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Dry package configuration

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{ "name": "my-package", "scripts": { "lint": "eslint ./src/*", "test": "jest ./src/*" } }

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{ "name": "my-package", "config": { "src": "./src/*" }, "scripts": { "lint": "eslint $npm_package_config_src", "test": "jest $npm_package_config_src" } }

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{ "name": "my-package", "config": { "src": "./src/*" }, "scripts": { "lint": "eslint $npm_package_config_src", "test": "jest $npm_package_config_src" } } Avoid duplication

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{ "foo": "bar" "scripts": { "start": "node index.js" } }

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{ "foo": "bar" "scripts": { "start": "node index.js" } } // index.js console.log(process.env.npm_package_foo); // 'bar'

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And finally...

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function f() { try { return 'A'; } finally { return 'B'; } } f(); // ? 'B'

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function g() { try { throw new Error('Foo'); } catch( e ) { return 'A'; } finally { return 'B'; } } f(); // ? 'B'

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function h() { try { throw new Error('Foo'); } finally { return 'B'; } } h(); //? 'B' (without throwing exception)

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function i() { try { throw new Error('Foo'); } catch( e ) { throw new Error('Bar'); return 'A'; } finally { return 'B'; } } i(); //? 'B' (without throwing exception)

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“ If the finally block returns a value, this value becomes the return value of the entire try-catch-finally production, regardless of any return statements in the try and catch blocks.

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“ If the finally block returns a value, this value becomes the return value of the entire try-catch-finally production, regardless of any return statements in the try and catch blocks.

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77 documented learnings

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www.stefanjudis.com/today-i-learned

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It only takes 
 10 minutes

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Did I improve? Like, at all? Oh yes!!!

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I'm building my own knowledge base!

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Celebrate learnings!

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Huh!
 I didn't know that!

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THANKS FOR LISTENING! @stefanjudis www.stefanjudis.com my-links.online/i-didnt-know

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THANKS FOR LISTENING! @stefanjudis www.stefanjudis.com my-links.online/i-didnt-know Yes, I bought my-links.online

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THANKS FOR LISTENING! @stefanjudis www.stefanjudis.com my-links.online/i-didnt-know