JavaScript Unary Operators

Last Updated : 25 Nov, 2024

JavaScript Unary Operators work on a single operand and perform various operations, like incrementing/decrementing, evaluating data type, negation of a value, etc.

Unary Plus (+) Operator

The unary plus (+) converts an operand into a number, if possible. It is commonly used to ensure numerical operations on variables that may contain numeric strings. If the operand is a string that represents a valid number, it will be converted to a number. Otherwise, it will evaluate to NaN (Not-a-Number).

JavaScript

let s1 = "12";

// Using unary plus to convert string to number
let x = +s1;
console.log(x);

// Here we are using typeof operator
console.log(typeof (x))

// "Geeks" cannot be converted to a number
let s2 = +"Geeks";
console.log(s2);

Output

12
number
NaN

Unary Minus (-) Operator

The Unary Negation (-) operator is used to convert its operand to a negative number if it isn’t already a negative number.

JavaScript

let s1 = "12";

// Unary negation, negates the
// value of number
let x = -s1;

console.log(x);

// Unary negation, tries to convert
// 'Geeks' to a number
let s2 = -"Geeks";

console.log(s2);

Output

-12
NaN

Unary Increment (++) Operator

The unary increment operator (++) adds 1 to its operand’s value and evaluates to the updated value. It can be used as a postfix or prefix operator.

Postfix: In postfix, the current value of the variable is used in the expression, and then the variable’s value is incremented by 1.
Prefix: In prefix, the variable’s value is first incremented by 1, and then the updated value is used in the expression.

JavaScript

// Case 1: Postfix
let x = 12;
let y = x++;
console.log(x);
console.log(y);

// Case 2: Preifix
x = 10;
y = ++x;
console.log(x);
console.log(y);

Output

Unary Decrement (–) Operator

The unary decrement operator (–) subtracts 1 from its operand’s value and evaluates it to the updated value, and we can use it as a postfix or prefix operator.

Postfix: In postfix form, the current value of the variable is used in the expression, and then the variable’s value is decremented by 1.
Prefix: In prefix form, the variable’s value is first decremented by 1, and then the updated value is used in the expression.

JavaScript

let x = 8;
let y = x--;
console.log(x);
console.log(y);

x = 15;
y = --x;
console.log(x);
console.log(y);

Output

Logical NOT (!) Operator

The logical NOT (!) is a unary operator that negates the Boolean value of an operand, converting true to false and false to true.

JavaScript

let x = false;
let y = !x;
console.log(y);

x = true;
y = !x;
console.log(y);

Output

true
false

Bitwise NOT (~) Operator

The bitwise NOT (~) is a unary operator that inverts all the bits of its operand, converting each 0 to 1 and each 1 to 0.

JavaScript

let x = 10;

// Bitwise NOT, inverts all bits of 'num'
let y = ~x;

console.log(y);

Output

-11

typeof Operator

The JavaScript typeof operator returns the data type of its operand in the form of a string. The operand can be any object, function, or variable.

JavaScript

let x = 18;
let s = "GeeksforGeeks";
let isTrue = true;
let obj = { name: "Aman", age: 21 };
let undefinedVar;

console.log(typeof x);
console.log(typeof s);
console.log(typeof isTrue);
console.log(typeof obj);
console.log(typeof undefinedVar);

Output

number
string
boolean
object
undefined

delete Operator

The delete operator in JavaScript removes a property from an object. If no other references exist, the property’s memory is automatically released.

JavaScript

let person = {
    name: "Ankit",
    age: 21,
    city: "Noida"
};

console.log(person);

delete person.age;

console.log(person);

Output

{ name: 'Ankit', age: 21, city: 'Noida' }
{ name: 'Ankit', city: 'Noida' }

void Operator

The void operator evaluates the given expression and then returns undefined.

JavaScript

function myFunction() {
    return void 0;
}
console.log(myFunction());

Output

undefined