Logical OR (||) - JavaScript | MDN

Toggle sidebar

Theme

OS default
Light
Dark

English (US)

Remember language Learn more

Logical OR (||)

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.

The logical OR (||) (logical disjunction) operator for a set of operands is true if and only if one or more of its operands is true. It is typically used with boolean (logical) values. When it is, it returns a Boolean value. However, the || operator actually returns the value of one of the specified operands, so if this operator is used with non-Boolean values, it will return a non-Boolean value.

Try it

const a = 3;
const b = -2;

console.log(a > 0 || b > 0);
// Expected output: true

Syntax

x || y

Description

If x can be converted to true, returns x; else, returns y.

If a value can be converted to true, the value is so-called truthy. If a value can be converted to false, the value is so-called falsy.

Examples of expressions that can be converted to false are:

null;
NaN;
0;
empty string ("" or '' or ``);
undefined.

Even though the || operator can be used with operands that are not Boolean values, it can still be considered a boolean operator since its return value can always be converted to a boolean primitive. To explicitly convert its return value (or any expression in general) to the corresponding boolean value, use a double NOT operator or the Boolean() constructor.

Short-circuit evaluation

The logical OR expression is evaluated left to right, it is tested for possible "short-circuit" evaluation using the following rule:

(some truthy expression) || expr is short-circuit evaluated to the truthy expression.

Short circuit means that the expr part above is not evaluated, hence any side effects of doing so do not take effect (e.g., if expr is a function call, the calling never takes place). This happens because the value of the operator is already determined after the evaluation of the first operand. See example:

js
function A() {
  console.log("called A");
  return false;
}
function B() {
  console.log("called B");
  return true;
}

console.log(B() || A());
// Logs "called B" due to the function call,
// then logs true (which is the resulting value of the operator)

Operator precedence

The following expressions might seem equivalent, but they are not, because the && operator is executed before the || operator (see operator precedence).

js
true || false && false; // returns true, because && is executed first
(true || false) && false; // returns false, because grouping has the highest precedence

Examples

Using OR

The following code shows examples of the || (logical OR) operator.

js
true || true; // t || t returns true
false || true; // f || t returns true
true || false; // t || f returns true
false || 3 === 4; // f || f returns false
"Cat" || "Dog"; // t || t returns "Cat"
false || "Cat"; // f || t returns "Cat"
"Cat" || false; // t || f returns "Cat"
"" || false; // f || f returns false
false || ""; // f || f returns ""
false || varObject; // f || object returns varObject

Note: If you use this operator to provide a default value to some variable, be aware that any falsy value will not be used. If you only need to filter out null or undefined, consider using the nullish coalescing operator.

Conversion rules for booleans

Converting AND to OR

The following operation involving booleans:

bCondition1 && bCondition2

is always equal to:

!(!bCondition1 || !bCondition2)

Converting OR to AND

The following operation involving booleans:

bCondition1 || bCondition2

is always equal to:

!(!bCondition1 && !bCondition2)

Removing nested parentheses

As logical expressions are evaluated left to right, it is always possible to remove parentheses from a complex expression following some rules.

The following composite operation involving booleans:

bCondition1 && (bCondition2 || bCondition3)

is always equal to:

!(!bCondition1 || !bCondition2 && !bCondition3)

Specifications

Specification

ECMAScript® 2027 Language Specification
# prod-LogicalORExpression

Browser compatibility

Enable JavaScript to view this browser compatibility table.

Help improve MDN

Was this page helpful to you?

Yes No

Learn how to contribute

This page was last modified on Jul 8, 2025 by MDN contributors.

View this page on GitHub • Report a problem with this content

Logical OR (||)

In this article

Try it

Syntax

Description

Short-circuit evaluation

Operator precedence

Examples

Using OR

Conversion rules for booleans

Converting AND to OR

Converting OR to AND

Removing nested parentheses

Specifications

Browser compatibility

See also

Help improve MDN