3 Ways to Set Default Value in JavaScript

3 Ways to Set Default Value in JavaScript

Let's break down the 3 different ways to set Default Values using logical operator, ternary, and if/else

Let's break down the 3 different ways to set Default Values using logical operator, ternary, and if/else

My go-to has always been the ternary operator for assigning a value to a variable conditionally. But ever since I discovered that “||” can be used as a selector operator, I’ve been using that more. I find my code so much easier to read 👍

Yes, it takes some time to wrap your head around it. But once you grasp the concept, it’s super handy. Now I don’t think less code makes your code better. But in this instance, I prefer the || operator 🤩

let isHappyHour = '🍺';

// Logical Operator
isHappyHour = isHappyHour || '🍵'; // '🍺'

// Ternary
isHappyHour = isHappyHour ? isHappyHour : '🍵'; // '🍺'

// If/Else
if (isHappyHour) { 
  isHappyHour = isHappyHour 
} else { 
  isHappyHour = '🍵' 
}

console.log(isHappyHour); // '🍺'


Understanding the || Operator

I’m sure most of you thought the || is only used for boolean checks like this:

if(a || b) {
  // do something
}


BUT! You can also use it to evaluate the selected expression and produce a value. And that’s why it’s helpful to think of the logical operator as also a selector operator. When it’s used with non-boolean values, the || operator will return a non-boolean value of one of the specified expression or operands.

Head explosion yet?! No worries, let me explain it the way Kyle Simpson explains it. He is the author of “You Don’t Know JavaScript” - a free JavaScript e-book.

The value produced by a && or || operator is not necessarily of type Boolean. The value produced will always be the value of one of the two operand expressions.
Alright, let’s look at an example.

const truthy = true;
const falsy = false;
const poop = '💩';

truthy || poop; // true
falsy || poop; // '💩';


As long as the 1st expression (left side) is truthy, it will always be the one selected. However, if the 1st expression (left side) is ever falsy, then the 2nd expression (right side) will be by default output. And that’s why this || is known as the operator to set default values.

Using Default Value as Function Parameter

Quite often you would see || being used like this:

function(name) {
  name = name || 'no name';
}


Note: this is not the recommended way anymore. It’s way better to ES6’s default parameters. Because quite often, you might not want the default to kick in for ALL falsy values – I’ll explain falsy values in the next section. Most likely, we only want the default value to be set if no value or undefined is passed as the argument.

The better solution with ES6 Default Parameters

function(name = 'no name') {
}


Falsy Values

In the || operator, the 2nd expression (right side) is only evaluated IF the 1st expression (left side). So let’s check what constitutes a falsy value.

// JS Essentials: Falsy Values

false
undefined
null
NaN
0
"" or '' or `` (empty string)


(I wrote another blog post on Falsy Values, which you can read it here)

Compared to the && operator

In my previous post, I wrote about the && operator. (Read it here). The && is also known as the Guard Operator. So here’s a quick summary of the difference:

  • ||: 1st expression is always outputted. The 2nd expression only gets outputted if the 1st expression is falsy.
  • &&: 1st expression is outputted if it’s FALSY. The 2nd expression only get outputted if the 1st expression is truthy.
What is the Elvis Operator

This is an interesting one. In JavaScript we have || to set default values. In other languages such as C++, this behavior is similar to the Elvis Operator which is denoted as ?:.

// JavaScript
someVariable || 'default value'

// Elvis Operator (not JavaScript)
someVariable ?: 'default value'


As to why it’s called the Elvis Operator:

*Image Credit to *GlobalNerdy.com

When to use which?

Now that you understand Falsy Values, let’s figure out which way of the 3 ways is better to use.

**🏆Logical Operator ****||**

This is great if you want to capture all falsy values. It’s less code and it’s way easier to read. Assuming that everyone understands all 3 behaviors, of course.

NOTE: I’m not saying less code is always better, one can easily try to be too clever and shorten the code which renders it unreadable. We write code for others, it’s a form of communication. It’s always better to go with the option that conveys understanding over being clever.

let a;

// ✅ Short and simple
a = a || b;

// ☹️ Meh, could be better
a = a ? a : b;

// 😱 Ouch
if (a) {
  a = a;
} else {
  a = b;
}


🏆Ternary Operator

Let’s say we don’t want to capture ALL falsy values. And we only want the default value to kick in when it’s undefined

// ❌ Logical doesn't work
a = (a === undefined) || b;
// (a === undefined) > will output a boolean 'true' not the actual value

// ✅ Ternary works
a = (a === undefined) ? a : b;

// ☹️ Of course if/else will also work...but Ouch
if (a === undefined) {
  a = a;
} else {
  a = b;
}


🏆If/Else

This is the option with the MOST control. And it’s something I would absolutely go for if say, I need to perform an additional action.

// ✅ If/Else is much better
if (a) {
  a = a;
  // do something else
} else {
  a = b;
}


Resources
  • ||: 1st expression is always outputted. The 2nd expression only gets outputted if the 1st expression is falsy.
  • &&: 1st expression is outputted if it’s FALSY. The 2nd expression only get outputted if the 1st expression is truthy.

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JavaScript developers should you be using Web Workers?

JavaScript developers should you be using Web Workers?

Do you think JavaScript developers should be making more use of Web Workers to shift execution off of the main thread?

Originally published by David Gilbertson at https://medium.com

So, Web Workers. Those wonderful little critters that allow us to execute JavaScript off the main thread.

Also known as “no, you’re thinking of Service Workers”.

Photo by Caleb Jones on Unsplash

Before I get into the meat of the article, please sit for a lesson in how computers work:

Understood? Good.

For the red/green colourblind, let me explain. While a CPU is doing one thing, it can’t be doing another thing, which means you can’t sort a big array while a user scrolls the screen.

This is bad, if you have a big array and users with fingers.

Enter, Web Workers. These split open the atomic concept of a ‘CPU’ and allow us to think in terms of threads. We can use one thread to handle user-facing work like touch events and rendering the UI, and different threads to carry out all other work.

Check that out, the main thread is green the whole way through, ready to receive and respond to the gentle caress of a user.

You’re excited (I can tell), if we only have UI code on the main thread and all other code can go in a worker, things are going to be amazing (said the way Oprah would say it).

But cool your jets for just a moment, because websites are mostly about the UI — it’s why we have screens. And a lot of a user’s interactions with your site will be tapping on the screen, waiting for a response, reading, tapping, looking, reading, and so on.

So we can’t just say “here’s some JS that takes 20ms to run, chuck it on a thread”, we must think about where that execution time exists in the user’s world of tap, read, look, read, tap…

I like to boil this down to one specific question:

Is the user waiting anyway?

Imagine we have created some sort of git-repository-hosting website that shows all sorts of things about a repository. We have a cool feature called ‘issues’. A user can even click an ‘issues’ tab in our website to see a list of all issues relating to the repository. Groundbreaking!

When our users click this issues tab, the site is going to fetch the issue data, process it in some way — perhaps sort, or format dates, or work out which icon to show — then render the UI.

Inside the user’s computer, that’ll look exactly like this.

Look at that processing stage, locking up the main thread even though it has nothing to do with the UI! That’s terrible, in theory.

But think about what the human is actually doing at this point. They’re waiting for the common trio of network/process/render; just sittin’ around with less to do than the Bolivian Navy.

Because we care about our users, we show a loading indicator to let them know we’ve received their request and are working on it — putting the human in a ‘waiting’ state. Let’s add that to the diagram.

Now that we have a human in the picture, we can mix in a Web Worker and think about the impact it will have on their life:

Hmmm.

First thing to note is that we’re not doing anything in parallel. We need the data from the network before we process it, and we need to process the data before we can render the UI. The elapsed time doesn’t change.

(BTW, the time involved in moving data to a Web Worker and back is negligible: 1ms per 100 KB is a decent rule of thumb.)

So we can move work off the main thread and have a page that is responsive during that time, but to what end? If our user is sitting there looking at a spinner for 600ms, have we enriched their experience by having a responsive screen for the middle third?

No.

I’ve fudged these diagrams a little bit to make them the gorgeous specimens of graphic design that they are, but they’re not really to scale.

When responding to a user request, you’ll find that the network and DOM-manipulating part of any given task take much, much longer than the pure-JS data processing part.

I saw an article recently making the case that updating a Redux store was a good candidate for Web Workers because it’s not UI work (and non-UI work doesn’t belong on the main thread).

Chucking the data processing over to a worker thread sounds sensible, but the idea struck me as a little, umm, academic.

First, let’s split instances of ‘updating a store’ into two categories:

  1. Updating a store in response to a user interaction, then updating the UI in response to the data change
  2. Not that first one

If the first scenario, a user taps a button on the screen — perhaps to change the sort order of a list. The store updates, and this results in a re-rendering of the DOM (since that’s the point of a store).

Let me just delete one thing from the previous diagram:

In my experience, it is rare that the store-updating step goes beyond a few dozen milliseconds, and is generally followed by ten times that in DOM updating, layout, and paint. If I’ve got a site that’s taking longer than this, I’d be asking questions about why I have so much data in the browser and so much DOM, rather than on which thread I should do my processing.

So the question we’re faced with is the same one from above: the user tapped something on the screen, we’re going to work on that request for hopefully less than a second, why would we want to make the screen responsive during that time?

OK what about the second scenario, where a store update isn’t in response to a user interaction? Performing an auto-save, for example — there’s nothing more annoying than an app becoming unresponsive doing something you didn’t ask it to do.

Actually there’s heaps of things more annoying than that. Teens, for example.

Anyhoo, if you’re doing an auto-save and taking 100ms to process data client-side before sending it off to a server, then you should absolutely use a Web Worker.

In fact, any ‘background’ task that the user hasn’t asked for, or isn’t waiting for, is a good candidate for moving to a Web Worker.

The matter of value

Complexity is expensive, and implementing Web Workers ain’t cheap.

If you’re using a bundler — and you are — you’ll have a lot of reading to do, and probably npm packages to install. If you’ve got a create-react-app app, prepare to eject (and put aside two days twice a year to update 30 different packages when the next version of Babel/Redux/React/ESLint comes out).

Also, if you want to share anything fancier than plain data between a worker and the main thread you’ve got some more reading to do (comlink is your friend).

What I’m getting at is this: if the benefit is real, but minimal, then you’ve gotta ask if there’s something else you could spend a day or two on with a greater benefit to your users.

This thinking is true of everything, of course, but I’ve found that Web Workers have a particularly poor benefit-to-effort ratio.

Hey David, why you hate Web Workers so bad?

Good question.

This is a doweling jig:

I own a doweling jig. I love my doweling jig. If I need to drill a hole into the end of a piece of wood and ensure that it’s perfectly perpendicular to the surface, I use my doweling jig.

But I don’t use it to eat breakfast. For that I use a spoon.

Four years ago I was working on some fancy animations. They looked slick on a fast device, but janky on a slow one. So I wrote fireball-js, which executes a rudimentary performance benchmark on the user’s device and returns a score, allowing me to run my animations only on devices that would render them smoothly.

Where’s the best spot to run some CPU intensive code that the user didn’t request? On a different thread, of course. A Web Worker was the correct tool for the job.

Fast forward to 2019 and you’ll find me writing a routing algorithm for a mapping application. This requires parsing a big fat GeoJSON map into a collection of nodes and edges, to be used when a user asks for directions. The processing isn’t in response to a user request and the user isn’t waiting on it. And so, a Web Worker is the correct tool for the job.

It was only when doing this that it dawned on me: in the intervening quartet of years, I have seen exactly zero other instances where Web Workers would have improved the user experience.

Contrast this with a recent resurgence in Web Worker wonderment, and combine that contrast with the fact that I couldn’t think of anything else to write about, then concatenate that combined contrast with my contrarian character and you’ve got yourself a blog post telling you that maybe Web Workers are a teeny-tiny bit overhyped.

Thanks for reading

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Further reading

An Introduction to Web Workers

JavaScript Web Workers: A Beginner’s Guide

Using Web Workers to Real-time Processing

How to use Web Workers in Angular app

Using Web Workers with Angular CLI