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

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