JavaScript

JavaScript Boolean Type

Truthy

We did say that Boolean only had two possible values: true or false. In JavaScript, we also have something called truthy and falsy values.

Truthy values are treated as true when used in a Boolean context (conditionals, etc).

Falsy values are treated as false when used in a Boolean context (conditionals, etc).

The general rule is that all JavaScript values are considered true unless they are one of the following values:

  • false: False is falsy; no surprises there.
  • 0, -0, 0n: The number zero is considered falsy.
  • "": The empty string is falsy.
  • null: Abscence of any object value is falsy.
  • undefined: Unassigned value is falsy.
  • NaN: Not a Number is falsy (result from possible invalid number operations).
// all false
const a = Boolean(false)
const b = Boolean(0)
const c = Boolean(-0)
const d = Boolean(0n)
const e = Boolean("")
const f = Boolean(null)
const g = Boolean(undefined)
const h = Boolean(NaN)
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