Unary plus (+)

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 unary plus (+) operator precedes its operand and evaluates to its operand but attempts to convert it into a number, if it isn't already.

Try it

const x = 1;
const y = -1;

console.log(+x);
// Expected output: 1

console.log(+y);
// Expected output: -1

console.log(+"");
// Expected output: 0

console.log(+true);
// Expected output: 1

console.log(+false);
// Expected output: 0

console.log(+"hello");
// Expected output: NaN

Although unary negation (-) also can convert non-numbers, unary plus is the fastest and preferred way of converting something into a number, because it does not perform any other operations on the number.

Unary plus does the exact same steps as normal number coercion used by most built-in methods expecting numbers. It can convert string representations of integers and floats, as well as the non-string values true, false, and null. Integers in both decimal and hexadecimal (0x-prefixed) formats are supported. Negative numbers are supported (though not for hex). If it cannot parse a particular value, it will evaluate to NaN. Unlike other arithmetic operators, which work with both numbers and BigInts, using the + operator on BigInt values throws a TypeError.

Examples

Usage with numbers

js
const x = 1;
const y = -1;

console.log(+x);
// 1
console.log(+y);
// -1

Usage with non-numbers

js
+true  // 1
+false // 0
+null  // 0
+[]    // 0
+function (val) { return val; } // NaN
+1n    // throws TypeError: Cannot convert BigInt value to number