What are the Logical Operators in JavaScript

There are four logical operators in JavaScript: || (OR), && (AND), ! (NOT), and ?? (Nullish Coalescing). They can be used with boolean values, or with non-boolean values.

OR (||) §

The OR operator (||) returns the first truthy value, or the last value if none are truthy.

console.log('hello' || 0); // hello
console.log(false || 'hello'); // hello
console.log('hello' || 'world'); // hello

AND (&&) §

The AND operator (&&) aka logical conjunction returns the first falsy value, or the last value if none are falsy.

console.log('hello' && 0); // 0
console.log(false && 'hello'); // false
console.log('hello' && 'world'); // world

NOT (!) §

It simply inverts the boolean value of its operand.

console.log(!true); // false
console.log(!false); // true
console.log(!'hello'); // false
console.log(!0); // true

Nullish Coalescing (??) §

The Nullish Coalescing Operator (??) returns the right operand if the left one is null or undefined, otherwise, it returns the left operand. It’s useful for setting default values without considering falsy values like 0 or '' as absent.

console.log(null ?? 'hello'); // hello
console.log(undefined ?? 'hello'); // hello
console.log('' ?? 'hello'); // ''
console.log(0 ?? 'hello'); // 0