Verify whether the value is considered false, true, or null

Question

Verify whether the value is considered false, true, or null

When dealing with variables in JavaScript, I often need to determine if a variable is false, true, or null. If the variable is null or undefined, I want to assign an array to it by default. While this syntax works well in other languages, in JS assigning an array to myBool when the value is false can be tricky.

const boolFromBody = false;
const myBool = boolFromBody || [true, false];
console.log(myBool)

I found a workaround by checking only for null values:

const boolFromBody = null;
let otherBool = boolFromBody;
if (boolFromBody === null) {
  otherBool = [true, false]
}
console.log(otherBool);

Is there a more elegant way to handle this scenario in JavaScript?

javascript

Answer 1

Answer №1

Understanding the Nullish coalescing operator.

In programming, the nullish coalescing operator checks if a variable is either null or undefined and assigns it to a default value if it meets that condition. It's important to note that values like 0 or false are not considered as nullish and will not trigger the default assignment.

The nullish coalescing operator ?? functions similarly to the || logical OR operator but with a key difference in how it evaluates conditions. Instead of relying on "truthy" values, it specifically targets values that are strictly equal to either null or undefined.

let x = null;

let y = x ?? "default";

console.log(y);

Let's explore an example using false:

let x = false;

let y = x ?? "default";

console.log(y);

Answer 2

Understanding the Nullish coalescing operator.

In programming, the nullish coalescing operator checks if a variable is either null or undefined and assigns it to a default value if it meets that condition. It's important to note that values like 0 or false are not considered as nullish and will not trigger the default assignment.

The nullish coalescing operator ?? functions similarly to the || logical OR operator but with a key difference in how it evaluates conditions. Instead of relying on "truthy" values, it specifically targets values that are strictly equal to either null or undefined.

let x = null;

let y = x ?? "default";

console.log(y);

Let's explore an example using false:

let x = false;

let y = x ?? "default";

console.log(y);

Answer 3

Answer №2

If you're looking for a solution that ensures backwards compatibility without using the nullish coalescing operator, here's an alternative option. This approach, although more verbose, is supported by even IE6 and can be more convenient and accessible if you're not using Babel. Hope this helps!

const boolFromBody = null;
let myBool = boolFromBody == (null || undefined) && [true, false];
console.log(myBool);

const boolFromBody = undefined;
let myBool = boolFromBody == (null || undefined) && [true, false];
console.log(myBool);

const boolFromBody = false;
let myBool = boolFromBody == (null || undefined) && [true, false];
console.log(myBool);

Answer 4

If you're looking for a solution that ensures backwards compatibility without using the nullish coalescing operator, here's an alternative option. This approach, although more verbose, is supported by even IE6 and can be more convenient and accessible if you're not using Babel. Hope this helps!

const boolFromBody = null;
let myBool = boolFromBody == (null || undefined) && [true, false];
console.log(myBool);

const boolFromBody = undefined;
let myBool = boolFromBody == (null || undefined) && [true, false];
console.log(myBool);

const boolFromBody = false;
let myBool = boolFromBody == (null || undefined) && [true, false];
console.log(myBool);

Verify whether the value is considered false, true, or null

Answer №1

Answer №2

Similar questions

Vue.js: Optimize Webpack bundle by excluding core-js

View the picture in a web browser

A common inquiry regarding Vue: How to effectively incorporate fullpage.js wrapper with additional functionalities

Generating random numbers within specified character limits using Javascript and Selenium

Loading a .css file in advance using NextJS

Does AngularJS have a feature similar to jQuery.active?

The Art of Capturing Sound: Unleashing

Tips for clicking a .class a random number of times:

Tips on inserting javascript to modify the CSS class of a table data cell in a Flask WTF jinja2 table based on the cell's value

Component does not display dynamically created DOM elements

Maintain the expanded menu even after selecting a sub-item using jQuery

Interactive Thumbnail Selection for HTML5 Video

Manipulating divs by positioning them at the top, left, right, bottom, and center to occupy the entire visible portion of the page

Leveraging the power of AJAX with either jquery or plain javascript to parse nested JSON data and display the

Adjusting height in Google Maps to fill the remaining space

Navigating the intricacies of retrieving network errors within an AngularJS application requires a deep

How can I adjust the width of a handle/thumb for NoUiSlider?

Refine your search with a JSON object description in expressJS and UnderscoreJS

Exploring the functionality of JSON within the jQuery each method

Unregistering an event with AngularJS