JavaScript Logical Operators

Jun 10, 2019

Learn the JavaScript logical operators and (&&), or (||), and not (!), including short-circuit evaluation for guarding access and setting default values.

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JavaScript provides us 3 logical operators: and, or and not.

Logical and

Returns true if both operands are true:

<expression> && <expression>

For example:

a === true && b > 3

The cool thing about this operator is that the second expression is never executed if the first evaluates to false. Which has some practical applications, for example, to check if an object is defined before using it:

const car = { color: 'green' }
const color = car && car.color

Logical or

Returns true if at least one of the operands is true:

<expression> || <expression>

For example:

a === true || b > 3

This operator is very useful to fallback to a default value. For example:

const car = {}
const color = car.color || 'green'

makes color default to green if car.color is not defined.

Logical not (!)

Invert the value of a boolean:

let value = true
!value //false

Tagged: JavaScript · All topics

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