#program:

[jcmarchi]

All About JavaScript Loops

New Post has been published on https://thedigitalinsider.com/all-about-javascript-loops/

All About JavaScript Loops

Every programming language has loops. Loops perform an operation (i.e., a chunk of work) a number of times, usually once for every item in an array or list, or to simply repeat an operation until a certain condition is met.

JavaScript in particular has quite a few different types of loops. I haven’t even used all of them, so for my own curiosity, I thought I’d do a high-level overview of them. And as it turns out, there are pretty good reasons I haven’t used at least a couple of the different types.

So, for now let’s spend a while exploring the different types of loops, what we can do with each of one, and why you might use one over another. (You’ll think that little play on words is absolutely hilarious by the end.)

The while and do...while loops

First up is the while loop. It’s the most basic type of loop and has the potential to be the easiest to read and the fastest in many cases. It’s usually used for doing something until a certain condition is met. It’s also the easiest way to make an infinite loop or a loop that never stops. There is also the do...while statement. Really, the only difference is that the condition is checked at the end versus the beginning of each iteration.

// remove the first item from an array and log it until the array is empty let queue1 = ["a", "b", "c"]; while (queue1.length) let item = queue1.shift(); console.log(item); // same as above but also log when the array is empty let queue2 = []; do let item = queue2.shift() ?? "empty"; console.log(item); while (queue2.length);

The for loop

Next is the for loop. It should be the go to way to do something a certain number of times. If you need to repeat an operation, say, 10 times, then use a for loop instead. This particular loop may be intimidating to those new to programming, but rewriting the same loop in the while-style loop can help illustrate the syntax make it easier to stick in your mind.

// log the numbers 1 to 5 for (let i = 1; i <= 5; i++) console.log(i); // same thing but as a while loop let i = 1; // the first part of a for loop // the second while (i <= 5) console.log(i); i++; // the third ("end");

The for...of and for await...of loops

A for...of loop is the easiest way to loop through an array.

let myList = ["a", "b", "c"]; for (let item of myList) console.log(item);

They aren’t limited to arrays though. Technically they can iterate through anything that implements what is called an iterable protocol. There are a few built-in types that implement the protocol: arrays, maps, set, and string, to mention the most common ones, but you can implement the protocol in your own code. What you’d do is add a [Symbol.iterator] method to any object and that method should return an iterator. It’s a bit confusing, but the gist is that iterables are things with a special method that returns iterators; a factory method for iterators if you will. A special type of function called a generator is a function that returns both a iterable and iterator.

let myList = *[Symbol.iterator]() yield "a"; yield "b"; yield "c"; , ; for (let item of myList) console.log(item);

There is the async version of all the things I just mentioned: async iterables, async iterators, and async generators. You’d use an async iterable with for await...of.

async function delay(ms) return new Promise((resolve) => setTimeout(resolve, ms); ); // this time we're not making an iterable, but a generator async function* aNumberAMinute() let i = 0; while (true) // an infinite loop yield i++; // pause a minute await delay(60_000); // it's a generator, so we need to call it ourselves for await (let i of aNumberAMinute()) console.log(i); // stop after one hour if (i >= 59) break;

One unobvious thing about for await...of statement is that you can use it with non-async iterables and it will work just fine. The reverse, however, is not true; you can’t use async iterables with the for...of statement.

The forEach and map loops

While these are not technically loops per se, you can use them to iterate over a list.

Here is the thing about the forEach method. Historically it was much slower than using a for loop. I think in some cases that may not be true anymore, but if performance is a concern, then I would avoid using it. And now that we have for...of I’m not sure there is much reason to use it. I guess the only reason that it still may come up is if you have a function ready to use as the callback, but you could easily just call that same function from inside the body of for...of.

forEach also receives the index for each item though, so that may be a thing you need too. Ultimately, the decision to use it will probably come down to whether any other code you’re working with uses it, but I personally would avoid using it if I’m writing something new.

let myList = ["a", "b", "c"]; for (let item of myList) console.log(item); // but maybe if I need the index use forEach ["a", "b", "c"].forEach((item, index) => console.log(`$index: $item`); );

Meanwhile, map essentially converts one array into another. It still has the same performance impact that forEach has, but it is a bit nicer to read than the alternative. It’s certainly subjective though, and just like with forEach you’ll want to do what the rest of your other code is doing. You see it a ton in React and React-inspired libraries as the primary way to loop through an array and output a list of items within JSX.

function MyList(items) return ( <ul> items.map((item) => return <li>item</li>; ) </ul> );

The for...in loop

This list of loops in JavaScript wouldn’t be complete without mentioning the for...in statement because it can loop through the fields of an object. It visits fields that are inherited through the object’s prototype chain too, though, and I’ve honestly always avoided it for that reason.

That said, if you have an object literal, then for...in might be a viable way to iterate through the keys of that object. Also it’s worth noting that if you’ve been programming JavaScript for a long time, you may remember that the order of keys use to be inconsistent between browsers, but now the order is consistent. Any key that could be an array index (i.e., positive integers) will be first in ascending order, and then everything else in the order as authored.

let myObject = a: 1, b: 2, c: 3, ; for (let k in myObject) console.log(myObject[k]);

Wrapping up

Loops are something that many programmers use every day, though we may take them for granted and not think about them too much.

But when you step back and look at all of the ways we have to loop through things in JavaScript, it turns out there are several ways to do it. Not only that, but there are significant — if not nuanced — differences between them that can and will influence your approach to scripts.

[meowlicious-food]

Read Full recipe here 👉⋆🦋 {{Hawaiian Roll French Toast}}🦋⋆

[389]

PORTO ROCHA

[skynoctis]

Legendary Boulder ~ WrestlerCheetah

Next sketch for cheetahgirlmuscles‬ Another entry on the Mia cosplaying as Guilty Gear characters book~ I hope you like it

[bartleby-company]

(vía Another America 50 by Phillip Toledano)

[70sscifiart]

One of my favorites by Paul Lehr, used as a 1971 cover to "Earth Abides," by George R. Stewart. It's also in my upcoming art book!

[taizooo]

もともとは10年ほど前にTumblrにすごくハマっていて。いろんな人をフォローしたらかっこいい写真や色が洪水のように出てきて、もう自分で絵を描かなくて良いじゃん、ってなったんです。それで何年も画像を集めていって、そこで集まった色のイメージやモチーフ、レンズの距離感など画面構成を抽象化して、いまの感覚にアウトプットしています。画像の持つ情報量というものが作品の影響になっていますね。

映画『きみの色』山田尚子監督×はくいきしろい対談。嫉妬し合うふたりが語る、色と光の表現｜Tokyo Art Beat

[nevver]

No one wants to be here and no one wants to leave, Dave Smith (because)

[giftofgabber]

don’t call me whiny baby if you didn’t care about my whiny baby feelings already, which you didn’t care about!!! shocker!!!

[389]

PORTO ROCHA

[theroyalweekly]

--

[mellowlike]

齋藤飛鳥

[goodvibesandmemes]

GENERAL MEMES: Vampire/Immortal Themed 🩸🦇🌹

↳ Please feel free to tweak them.

Themes: violence, death, blood, murder, depression/negative thoughts

SYMBOLS: ↳ Use “↪”to reverse the characters where applicable!

🦇 - To catch my muse transforming into a bat 🌞 - To warn my muse about/see my muse in the sunlight. 🩸 - To witness my muse drinking blood from a bag. 🐇 - To witness To catch my muse drinking blood from an animal. 🧔🏽 - To witness To catch my muse drinking blood from a human. 🦌 - For our muses hunt together for the first time. 🏃🏿‍♀️ - To see my muse using super speed. 🏋🏼‍♂️ - To see my muse using their super strength. 🧛🏻‍♂️ - To confront my muse about being a vampire. 🌕 - For my muse to lament missing the sun. ⏰ - For my muse to tell yours about a story from their long, immortal life. 🤛🏽 - To offer my muse your wrist to drink from. 👩🏿 - For my muse to reminisce about a long lost love. 👩🏽‍🤝‍👩🏽 - For your muse to look exactly like my muse's lost love. 👄 - For my muse to bite yours. 👀 - For my muse to glamour/compel yours. 🧄 - To try and sneakily feed my muse garlic to test if they're a vampire. 🔗 - To try and apprehend my muse with silver chains. 🔪 - To try and attack my muse with a wooden stake. 👤 - To notice that my muse doesn't have a reflection. 🌹 - For my muse to turn yours into a vampire. 🌚 - For my muse and yours to spend time together during the night. 🧛🏼‍♀️ - For my muse to tell yours about their maker/sire.

SENTENCES:

"I've been alive for a long time [ name ], I can handle myself." "I'm over a thousand years old, you can't stop me!" "Lots of windows in this place, not exactly the greatest place for a vampire." "Do you really drink human blood? Don't you feel guilty?" "Vampires are predators, [ name ] hunting is just part of our nature, you can't change that." "You just killed that person! You're a monster!" "Tomorrow at dawn, you'll meet the sun [ name ]." "Can you make me like you?" "Do you really want to live forever?" "You say you want to live forever, [ name ], but forever is a long time, longer than you can imagine." "What was it like to live through [ historic event / time period ]?" "Did people really dress like that when you were young?" "What were you like when you were human?" "We’re vampires, [ name ], we have no soul to save, and I don’t care." "How many people have you killed? You can tell me, I can handle it." "Did you meet [ historic figure ]?" "Everyone dies in the end, what does it matter if I... speed it along." "Every time we feed that person is someone's mother, brother, sister, husband. You better start getting used to that if you want to survive this life." "[ she is / he is / they are ] the strongest vampire anyone has heard of, no one knows how to stop them, and if you try you're going to get yourselves killed." "Vampire hunters are everywhere in this city, you need to watch your back." "Humans will never understand the bond a vampire has with [ his / her / their ] maker, it's a bond like no other." "Here, have this ring, it will protect you from the sunlight." "I get you're an immortal creature of the night and all that, but do you have to be such a downer about it?" "In my [ centuries / decades / millennia ] of living, do you really think no one has tried to kill me before?" "Vampires aren't weakened by garlic, that's a myth." "I used to be a lot worse than I was now, [ name ], I've had time to mellow, to become used to what I am. I'm ashamed of the monster I was." "The worst part of living forever is watching everyone you love die, while you stay frozen, still, constant." "I've lived so long I don't feel anything any more." "Are there more people like you? How many?" "Life has never been fair, [ name ], why would start being fair now you're immortal?" "You want to be young forever? Knock yourself out, I just hope you understand what you're giving up." "You never told me who turned you into a vampire. Who were they? Why did they do it?" "I could spend an eternity with you and never get bored." "Do you really sleep in coffins?" "There are worse things for a vampire than death, of that I can assure you [ name ]." "You need to feed, it's been days. You can drink from me, I can tell you're hungry." "The process of becoming a vampire is risky, [ name ], you could die, and I don't know if I could forgive myself for killing you." "I'm a vampire, I can hold a grudge for a long time, so believe me when I say I will never forgive this. Never." "You were human once! How can you have no empathy?" "You don't have to kill to be a vampire, but what would be the fun in that." "You can spend your first years of immortality doing whatever you want to whoever you want, but when you come back to your senses, it'll hit you harder than anything you've felt before." "One day, [ name ], everything you've done is going to catch up to you, and you're never going to forgive yourself." "Stop kidding yourself, [ name ], you're a vampire, a killer, a predator. You might as well embrace it now because you can't keep this up forever." "You can't [ compel / glamour ] me, I have something to protect me." "When you've lived as long as me, there's not much more in life you can do." "You want me to turn you? You don't know what you're asking me to do." "You really have to stop hissing like that, it's getting on my nerves." "I'm going to drive this stake through your heart, [ name ], and I'm going to enjoy it."

[shitakeo33]

よく「発明は1人でできる。製品化には10人かかる。量産化には100人かかる」とも言われますが、実際に、私はネオジム磁石を1人で発明しました。製品化、量産化については住友特殊金属の仲間たちと一緒に、短期間のうちに成功させました。82年に発明し、83年から生産が始まったのですから、非常に早いです。そしてネオジム磁石は、ハードディスクのＶＣＭ(ボイスコイルモーター)の部品などの電子機器を主な用途として大歓迎を受け、生産量も年々倍増して、2000年には世界で1万トンを超えました。

世界最強「ネオジム磁石はこうして見つけた」（佐川眞人 氏 ／ インターメタリックス株式会社 代表取締役社長） | Science Portal - 科学技術の最新情報サイト「サイエンスポータル」

[nevver]

Arts & Architecture, Sander Patelski