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Cover image for JavaScript One-Liners That Make Me Excited
Andrew Healey
Andrew Healey

Posted on • Updated on • Originally published at healeycodes.com

JavaScript One-Liners That Make Me Excited

Dust off your ternary expressions, we're going in.

One-liners are tricky to maintain (and sometimes even hard to understand) but that doesn't stop them from being cool as hell. There's a certain satisfaction that comes after writing a terse solution.

This is a collection of some of my recent favorites. They will all run in your dev console so pop it open and try them out. I hope you'll share some of your own favorites in the comments!

Calendar Hacking

Ali Spittel tweeted this out recently. It solves a problem I've faced multiple times. If you swap the minus for a plus, it gives you the next seven days.

// Create an array of the past seven days, inclusive
[...Array(7).keys()].map(days => new Date(Date.now() - 86400000 * days));
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Random ID generation

This is my go-to function for creating unique ids when prototyping. I've even seen people using it in production in the past. It's not secure but ... there are worse random generation functions out there.

// Generate a random alphanumerical string of length 11
Math.random().toString(36).substring(2);
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Quines

A quine is a program that outputs its own source code. Quines have always fascinated me. I've got pretty close to completing my own quines a couple of times in different languages but details are the name of the game.

I've picked some winners for you. Credit to Mama Fun Roll, PleaseStand, and Peter Olson respectively for these three.

// $=_=>`$=${$};$()`;$()
$=_=>`$=${$};$()`;$()

// eval(I="'eval(I='+JSON.stringify(I)+')'")
eval(I="'eval(I='+JSON.stringify(I)+')'")

// For those who like their quines via alert
// (function a(){alert("("+a+")()")})()
(function a(){alert("("+a+")()")})()
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Scrape query parameters

Talk about non-maintainable code. This converts the page's query parameters to an object in 78 bytes. Thanks Alex Lohr for code golfing it (and 齐翊 too).

?foo=bar&baz=bing => {foo: bar, baz: bing}

// Set the current page's query parameters to `q`
q={};location.search.replace(/([^?&=]+)=([^&]*)/g,(_,k,v)=>q[k]=v);q;
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I'd like to see a minifier work that hard.

Working clock

With a sprinkle of HTML, you can create a working clock with source code you could read out in one breath. I wrote this after a challenge from a co-worker. It ticks every second, updating the page with the current time.

<body onload="setInterval(()=>document.body.innerHTML=new Date().toGMTString().slice(17,25))"></body>
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Shuffle an array

Until Pythonistas show up with their import random, random.shuffle(array) solution, we're going to enjoy what we have. This has the bonus of having an infinitesimal chance of being an infinite loop (implementation depending). Michiel Hendriks helped us save a few characters here πŸ‘. Don't use in production.

// Return a shuffled copy of an Array-like
(arr) => arr.slice().sort(() => Math.random() - 0.5)
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Generate random hex code

ES7's padEnd is a blessing. Along with padStart, they've made number to string conversions that much easier. Writing hex values right into JavaScript code is always pretty neat too.

// Generate a random hex code such as `#c618b2`
'#' + Math.floor(Math.random() * 0xffffff).toString(16).padEnd(6, '0');
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Pass the interview in style

The infamous interview question answer but codegolfed. I researched and I don't think it can get any shorter than this.

for(i=0;++i<101;console.log(i%5?f||i:f+'Buzz'))f=i%3?'':'Fizz'
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Remove duplicates

This only works with primitives but it's still nifty. Set takes any iterable object, like an array [1,2,3,3], and removes duplicates. The spread operator makes that set [1,2,3].

// Remove duplicates from the iterable `arr`
[...new Set(arr)]
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A keyboard so real you can taste it

Okay, I don't really count this as a one-liner but it's too good not to include. A masterful codegolf solution by edc65. It's terse to a fault and codegolfed within an inch of its life but we should bask in its glory.

// Return a ***3D*** ASCII keyboard as string
(_=>[..."`1234567890-=~~QWERTYUIOP[]\\~ASDFGHJKL;'~~ZXCVBNM,./~"].map(x=>(o+=`/${b='_'.repeat(w=x<y?2:' 667699'[x=["BS","TAB","CAPS","ENTER"][p++]||'SHIFT',p])}\\|`,m+=y+(x+'    ').slice(0,w)+y+y,n+=y+b+y+y,l+=' __'+b)[73]&&(k.push(l,m,n,o),l='',m=n=o=y),m=n=o=y='|',p=l=k=[])&&k.join`
`)()
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It prints:

Amazing.


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Top comments (56)

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michi profile image
Michael Z

I've got another good one to create arrays of a specific size and map over it at the same time.

Array.from({length: 3}, (val, i) => i)
// [0, 1, 2]
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dhe profile image
d-h-e
[...Array(3).keys()]
// [0, 1, 2]
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qm3ster profile image
Mihail Malo

Oh SHID.
This is exactly what I needed so many times, and it finally seems like it's a performant approach?!

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brian profile image
Brian • Edited on

It looks quite clean and sleek, so I decided to test out the performance on my pc

Weirdly using Array(N) is about 20% faster than using an array-like {length: N} when used inside Array.from()

I also added comparisons of mapping as a parameter vs (dot)map too.

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qm3ster profile image
Mihail Malo

Wow, that's... humbling.
BTW, you could beat out ForLoop with:

const arr = new Array(100)
for (let i = 0, i < 100, i++)
  arr[i] = i

since the size is known in advance.

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lexlohr profile image
Alex Lohr

You can shave off one more char for your hex color code generator without resorting to padEnd:

// before
'#' + Math.floor(Math.random() * 0xffffff).toString(16).padEnd(6, '0');

// after
'#' + (0x1000000 + Math.random() * 0xffffff).toString(16).slice(1, 6);
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healeycodes profile image
Andrew Healey Author

A clever change. Probably faster too?

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lexlohr profile image
Alex Lohr

Thanks. Not sure if it's faster, but that's usually a non-issue for code golfing :)

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rithvikvibhu profile image
Rithvik Vibhu

I was curious and created a test: jsperf.com/hex-color-code-generator
:)

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healeycodes profile image
Andrew Healey Author

Awesome! Close to what I expected πŸ‘

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moopet profile image
Ben Sinclair • Edited on
// I'd like to see a minifier work that hard.
document.location.search.replace(/(^\?)/,'').split('&').reduce(function(o,n){n=n.split('=');o[n[0]]=n[1];return o},{});

// Challenge accepted.
location.search.substr(1).split('&').reduce((o,n)=>{n=n.split('=');o[n[0]]=n[1];return o},{});
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I'm not a big Javascript person so I don't know what the difference is between window.location, document.location and just location (which I assume uses the global window context). I know substr works fine on an empty string, and I'm making the (heroically cavalier) assumption that query strings start with a ? in all browsers' implementations of location.search.

But both of these return something incorrect if there's no query string:

{"": undefined}
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Oops. Well, we can do something about that:

(() => {let x=location.search.substr(1).split('&').reduce((o,n)=>{n=n.split('=');o[n[0]]=n[1];return o},{});delete x[""];return x})()
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And now it's longer and even less maintainable, but hey :)

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healeycodes profile image
Andrew Healey Author

This is brilliant, Ben! πŸ˜„

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lexlohr profile image
Alex Lohr

I can probably do it in even less characters... let me try:

q={};document.location.search.replace(/([^?&=]+)=([^&]+)/g,(_,k,v)=>q[k]=v);q;
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luckybilly profile image
齐翊

Hey, that one could not accept empty value (eg:'?a=&b=1&c=')
try this instead:

//keys should not be empty, but value can
q={};location.search.replace(/([^?&=]+)=([^&]*)/g,(_,k,v)=>q[k]=v);q;
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chiangs profile image
Stephen Chiang

Awesome one liners... Until you hit save and Prettier formats it to two 🀣

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sabberworm profile image
Raphael Schweikert • Edited on

Be careful with that shuffle, it won’t yield truly random results because sort expects its comparator to uphold Math.sign(compare(a, b)) === -Math.sign(compare(b, a)). Microsoft once screwed up by using exactly that.

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healeycodes profile image
Andrew Healey Author

What an interesting story! Thanks for sharing.

And yes, for any production code just use Fisher/Yates!

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brianjenkins94 profile image
Brian Jenkins • Edited on

Does this count? 😈

{
    "precommit": "git ls-files | while read -r FILE; do if file \"$FILE\" | grep -q \"text\"; then vim --clean -n -e -s -c \":%s/\\s\\+$//e|:retab|:wq\" \"$FILE\"; fi ; done"
}
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healeycodes profile image
Andrew Healey Author

I'll allow it! πŸ˜€

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elmuerte profile image
Michiel Hendriks • Edited on

Why waste all those extra characters, this also works

(arr) => arr.slice().sort(() => Math.random() - 0.5)
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t0nyba11 profile image
Tony B • Edited on

Why waste all those extra characters, this also works :)

(a) => [...a].sort(() => Math.random() - 0.5)

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healeycodes profile image
Andrew Healey Author

Nice find, thanks! Edited πŸ‘.

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greg profile image
greg

It's a shorthand for returning one of three colors if the score is truthy. Otherwise it returns a fallback value.

score => ({1: "#98FB98", 2: "#FFFF99", 3: "#FA8072"}[score] || "#DCDCDC")
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lexlohr profile image
Alex Lohr

that can be even more minified:

score => (["", "#98FB98", "#FFFF99", "#FA8072"][score] || "#DCDCDC")

you could lose the first array item and use score - 1, but that would have more characters.

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kenbellows profile image
Ken Bellows

Would it? Wouldn't you shorten by 4 chars to remove "",, or 3 if whitespace doesn't count, and only add 2 chars to go from [score] to [score-1]? Seems like it'd still be shorter by at least a character, or am I missing something?

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jacobmgevans profile image
Jacob Evans • Edited on
isInRange = (a, b, c) => [...Array(c - a +1)].map((e, i) => i + a).indexOf(b) !== -1

I did this one for a challenge. It finds if a number is in a range of two other numbers so find if b is in range of a to c

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nestedsoftware profile image
Nested Software • Edited on

Wouldn't you just check b >= a && b <= c ?

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jacobmgevans profile image
Jacob Evans

That was definitely a way to do it. However, I am pretty sure that only works with constraints on the range values, and the way I wanted to solve it was to be sure it could handle any range.

I could be wrong which in that case, I will certainly remember this way lol

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jacobmgevans profile image
Jacob Evans

Nope to me lol, you're just right and I am pretty sure that works for any size range not just that but the
Big O is significantly better ahahaha!

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daksamit profile image
Dominik Aksamit

The one I recently discovered as very useful, mostly while testing or mocking API calls:

await new Promise((resolve) => setTimeout(() => resolve(1), 2500));
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Usually I use, when I have to simulate data fetching ;P

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t0nyba11 profile image
Tony B

Or more succinctly...

await new Promise(r => setTimeout(r, 2500))
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healeycodes profile image
Andrew Healey Author

Very cool! Thanks for sharing Dominik πŸ‘

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daksamit profile image
Dominik Aksamit

Thanks! I would recommend adding most of them to vscode snippets. It's really easy to use just like typing "sleep" + enter and I have ready one-liner in my code ;)

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lexlohr profile image
Alex Lohr

There are a lot of byte saving tips one can employ in code golfing. A nice collection can be found here: github.com/jed/140bytes/wiki/Byte-...

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korbraan profile image
CΓ©dric RΓ©mond

I use Set often to remove duplicates, but I didn't know it's possible to use the spread operator on a Set.

I have been using Array.from(new Set(myArray)) until now. Since Array.from take an iterable I could have guessed but...

Nice post !

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healeycodes profile image
Andrew Healey Author

Glad it helped ya!

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luckybilly profile image
齐翊 • Edited on
q={};location.search.replace(/([^?&=]+)=([^&]+)/g,(_,k,v)=>q[k]=v);q;

got a problem like this:

'?a=&b=1&c='  ----> {b: 1} 

lost key 'a' and 'c'

solution: replace the 2nd '+' by '*'

q={};location.search.replace(/([^?&=]+)=([^&]*)/g,(_,k,v)=>q[k]=v);q;
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healeycodes profile image
Andrew Healey Author • Edited on

Thanks! Fixed it :)

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kelerchian profile image
Alan
const makeMockingSpongebobMeme = (someString) => (typeof someString === "string" ? someString : "Wrong input").split("").map(a => Math.random() > 0.5 ? a.toLowerCase() : a.toUpperCase()).join("")

One of the intriguing trait of functional programming is to look unreadable despite being working.

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qm3ster profile image
Mihail Malo • Edited on
const r = {valueOf: Math.random}

Not really a one-liner, but good for when making generative art.

Take a look at this:

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