Boolean values
Learn true and false values and expressions that return booleans.
Boolean values
In JavaScript the boolean type holds only two values: true and false. These values represent binary states such as whether a button is on or off, or whether a user is signed in.
You declare a boolean variable with let or const: const isOpen = true;. Comparison operators also return booleans: 5 > 3 gives true, 5 < 3 gives false. Such expressions are called boolean expressions.
Comparisons return booleans
Comparison operators compare two values and always return a boolean. Common operators are === (equal), !== (not equal), > (greater), < (less), >= and <=.
For example 10 === 10 gives true while "5" === 5 gives false, because === compares both value and type. The typeof operator returns the type name: typeof true is "boolean". This lets you check whether a value is a boolean.
Exercise Create boolean variables
Set isLoggedIn to false and hasPermission to true. Print both with console.log.
Show example solution
const isLoggedIn = false;
const hasPermission = true;
console.log(isLoggedIn);
console.log(hasPermission);Exercise Write comparison expressions
Set age to 20. Set canVote to the comparison age >= 18. Set isMinor to the comparison age < 18. Print both.
Show example solution
const age = 20;
const canVote = age >= 18;
const isMinor = age < 18;
console.log(canVote);
console.log(isMinor);Test yourself
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Which is a boolean value?
- true
- "hello"
- 42
- null
Show answer
true — Correct. true is a boolean value.
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Declare a boolean variable
const isReady = ____; console.log(isReady);Show answer
const isReady = true; console.log(isReady);